Earnings Per Share - Computation of Basic and Diluted Net Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net income	$ 45,380	$ 39,152	$ 48,762	$ 47,282	$ 31,414	$ 28,769	$ 35,722	$ 41,160	$ 180,576	$ 137,065	$ 123,486
Less: income allocable to participating securities									(81)	(159)	(315)
Income allocable to common shares									180,495	136,906	123,171
Add back: undistributed earnings allocable to participating securities									81	159	315
Less: undistributed earnings reallocated to participating securities									(80)	(156)	(310)
Numerator for diluted earnings per share									$ 180,496	$ 136,909	$ 123,176
Denominator:
Basic weighted average shares outstanding	57,659	57,654	57,569	57,357	57,491	57,727	57,837	57,793	57,561	57,711	57,839
Dilutive effect of unvested restricted stock									834	871	951
Diluted weighted average shares outstanding	58,378	58,383	58,410	58,316	58,238	58,545	58,721	58,739	58,395	58,582	58,790
Earnings per share:
Earnings per share, basic	$ 0.79	$ 0.68	$ 0.85	$ 0.82	$ 0.55	$ 0.50	$ 0.62	$ 0.71	$ 3.14	$ 2.37	$ 2.13
Earnings per share, diluted	$ 0.78	$ 0.67	$ 0.83	$ 0.81	$ 0.54	$ 0.49	$ 0.61	$ 0.70	$ 3.09	$ 2.34	$ 2.10