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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator:
Net income	$ 35,722	$ 20,016	$ 76,882	$ 53,710
Less: income allocable to participating securities	(83)	(69)	(179)	(187)
Income allocable to common shares	35,639	19,947	76,703	53,523
Add back: undistributed earnings allocable to participating securities	83	69	179	187
Less: undistributed earnings reallocated to participating securities	(82)	(68)	(176)	(183)
Numerator for diluted earnings per share	$ 35,640	$ 19,948	$ 76,706	$ 53,527
Denominator:
Basic weighted average shares outstanding	57,837,312	57,898,914	57,815,290	57,623,107
Dilutive effect of unvested restricted stock	883,473	917,528	951,613	1,194,074
Diluted weighted average shares outstanding	58,720,785	58,816,442	58,766,903	58,817,181
Earnings per share:
Earnings per share, basic	$ 0.62	$ 0.34	$ 1.33	$ 0.93
Earnings per share, diluted	$ 0.61	$ 0.34	$ 1.31	$ 0.91