Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator:
Net income	$ 14,221	$ 10,421	$ 39,835	$ 29,009
Less: income allocable to participating securities	(49)	(129)	(138)	(360)
Income allocable to common shares	14,172	10,292	39,697	28,649
Add back: undistributed earnings allocable to participating securities	49	129	138	360
Less: undistributed earnings reallocated to participating securities	(48)	(126)	(136)	(360)
Numerator for diluted earnings per share	$ 14,173	$ 10,295	$ 39,699	$ 28,649
Denominator:
Weighted average common shares outstanding	50,315,455	50,315,455	50,315,455	50,315,455
Weighted average common shares repurchased	(1,277,102)	(19,969)	(1,200,109)	(9,985)
Adjustment for vested restricted stock	8,860,561	7,296,070	8,507,761	7,056,762
Shares for calculating basic earnings per share	57,898,914	57,591,556	57,623,107	57,362,232
Dilutive effect of unvested restricted stock	917,528	1,105,673	1,194,074	1,344,981
Shares for calculating diluted earnings per share	58,816,442	58,697,229	58,817,181	58,707,213
Earnings per share:
Basic	$ 0.24	$ 0.18	$ 0.69	$ 0.50
Diluted	$ 0.24	$ 0.18	$ 0.67	$ 0.49