Earnings Per Share - Computation of Basic and Diluted Net Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Numerator:
Net income	$ 47,282	$ 41,160
Less: income allocable to participating securities	(55)	(100)
Income allocable to common shares	47,227	41,060
Add back: undistributed earnings allocable to participating securities	55	100
Less: undistributed earnings reallocated to participating securities	(54)	(98)
Numerator for diluted earnings per share	$ 47,228	$ 41,062
Denominator:
Basic weighted average shares outstanding	57,357,490	57,793,023
Dilutive effect of unvested restricted stock	958,664	945,709
Diluted weighted average shares outstanding	58,316,154	58,738,732
Earnings per share:
Earnings per share, basic	$ 0.82	$ 0.71
Earnings per share, diluted	$ 0.81	$ 0.70