Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Monthly Distributions Declared and Paid by Company's Board of Directors (Detail)

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Stockholders' Equity - Monthly Distributions Declared and Paid by Company's Board of Directors (Detail) - $ / shares
6 Months Ended
Jun. 30, 2015
May. 28, 2015
May. 04, 2015
Mar. 31, 2015
Feb. 27, 2015
Feb. 03, 2015
Jun. 30, 2014
May. 30, 2014
Apr. 30, 2014
Mar. 31, 2014
Feb. 28, 2014
Jan. 31, 2014
Jun. 30, 2015
Jun. 30, 2014
Class of Stock [Line Items]                            
Distributions per Common Share                         $ 0.225 $ 0.180
Monthly Distribution One [Member]                            
Class of Stock [Line Items]                            
Dividend Declaration Date                         Jan. 13, 2015 Jan. 07, 2014
Record Date                         Jan. 23, 2015 Jan. 22, 2014
Dividend Payment Date                         Feb. 03, 2015 Jan. 31, 2014
Distributions per Common Share           $ 0.035           $ 0.030    
Monthly Distribution Two [Member]                            
Class of Stock [Line Items]                            
Dividend Declaration Date                         Jan. 13, 2015 Jan. 07, 2014
Record Date                         Feb. 18, 2015 Feb. 19, 2014
Dividend Payment Date                         Feb. 27, 2015 Feb. 28, 2014
Distributions per Common Share         $ 0.035           $ 0.030      
Monthly Distribution Three [Member]                            
Class of Stock [Line Items]                            
Dividend Declaration Date                         Jan. 13, 2015 Jan. 07, 2014
Record Date                         Mar. 20, 2015 Mar. 17, 2014
Dividend Payment Date                         Mar. 31, 2015 Mar. 31, 2014
Distributions per Common Share       $ 0.035           $ 0.030        
Monthly Distribution Four [Member]                            
Class of Stock [Line Items]                            
Dividend Declaration Date                         Apr. 14, 2015 Apr. 08, 2014
Record Date                         Apr. 24, 2015 Apr. 21, 2014
Dividend Payment Date                         May 04, 2015 Apr. 30, 2014
Distributions per Common Share     $ 0.040           $ 0.030          
Monthly Distribution Five [Member]                            
Class of Stock [Line Items]                            
Dividend Declaration Date                         Apr. 14, 2015 Apr. 08, 2014
Record Date                         May 19, 2015 May 20, 2014
Dividend Payment Date                         May 28, 2015 May 30, 2014
Distributions per Common Share   $ 0.040           $ 0.030            
Monthly Distribution Six [Member]                            
Class of Stock [Line Items]                            
Dividend Declaration Date                         Apr. 14, 2015 Apr. 08, 2014
Record Date                         Jun. 19, 2015 Jun. 19, 2014
Dividend Payment Date                         Jun. 30, 2015 Jun. 30, 2014
Distributions per Common Share $ 0.040           $ 0.030