Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net income	$ 28,769	$ 20,910	$ 105,651	$ 74,620
Less: income allocable to participating securities	(36)	(58)	(134)	(207)
Income allocable to common shares	28,733	20,852	105,517	74,413
Add back: undistributed earnings allocable to participating securities	36	58	134	207
Less: undistributed earnings reallocated to participating securities	(36)	(57)	(132)	(203)
Numerator for diluted earnings per share	$ 28,733	$ 20,853	$ 105,519	$ 74,417
Denominator:
Basic weighted average shares outstanding	57,726,790	58,003,222	57,785,466	57,751,204
Dilutive effect of unvested restricted stock	818,271	870,280	938,762	1,088,567
Diluted weighted average shares outstanding	58,545,061	58,873,502	58,724,228	58,839,771
Earnings per share:
Earnings per share, basic	$ 0.50	$ 0.36	$ 1.83	$ 1.29
Earnings per share, diluted	$ 0.49	$ 0.35	$ 1.80	$ 1.26