Earnings Per Share - Computation of Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Numerator:
Net income to common shareholders	$ 131,461	$ 175,722	$ 163,356
Net income allocated to participating securities - basic and diluted	2,895	3,631	3,105
Net income allocated to common shareholders - basic and diluted	$ 128,566	$ 172,091	$ 160,251
Denominator:
Weighted-average common shares - basic	78,197	81,804	83,066
Dilutive potential common shares	110	230	101
Weighted average common shares - diluted	78,307	82,034	83,167
Earnings per common share:
Basic	$ 1.64	$ 2.10	$ 1.93
Diluted	$ 1.64	$ 2.10	$ 1.93