Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Numerator:
Net income	$ 41,160	$ 33,694
Less: income allocable to participating securities	(100)	(254)
Income allocable to common shares	41,060	33,440
Add back: undistributed earnings allocable to participating securities	100	254
Less: undistributed earnings reallocated to participating securities	(98)	(249)
Numerator for diluted earnings per share	$ 41,062	$ 33,445
Denominator:
Weighted average common shares outstanding	50,315,455	50,315,455
Weighted average common shares repurchased	(2,408,586)	(1,122,261)
Adjustment for vested restricted stock	9,886,154	8,113,993
Shares for calculating basic earnings per share	57,793,023	57,307,187
Dilutive effect of unvested restricted stock	945,709	1,218,793
Shares for calculating diluted earnings per share	58,738,732	58,525,980
Earnings per share:
Earnings per share, basic	$ 0.71	$ 0.58
Earnings per share, diluted	$ 0.70	$ 0.57