Earnings Per Share - Computation of Basic Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Calculation Of Numerator And Denominator In Earnings Per Share [Line Items]
Allocation of net income (loss) to common stock	$ 22,510	$ 20,558	$ 77,640	$ 70,009
Earnings (loss) per share:
Common stock-basic (usd per share)	$ 0.38	$ 0.34	$ 1.30	$ 1.14
Common Stock [Member]
Calculation Of Numerator And Denominator In Earnings Per Share [Line Items]
Allocation of net income (loss) to common stock	$ 22,306	$ 20,415	$ 76,954	$ 69,536
Weighted average number of common shares:
Weighted average number (shares)	58,928,264	60,290,842	59,326,525	61,112,263
Unvested Participating Shares [Member]
Calculation Of Numerator And Denominator In Earnings Per Share [Line Items]
Allocation of net income (loss) to common stock	$ 204	$ 143	$ 686	$ 473
Weighted average number of common shares:
Weighted average number (shares)	538,795	422,725	528,887	415,472