Summary of Significant Accounting Policies (Reconciliation of Numerators and Denominators of Basic and Diluted Earnings Per Share Calculations) (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
Accounting Policies [Abstract]
Net income	$ 22,906	$ 20,609	$ 65,235	$ 62,207
Income available to common stockholders, basic	22,906	20,609	65,235	62,207
Income available to common stockholders, diluted	$ 22,906	$ 20,609	$ 65,235	$ 62,207
Weighted average common shares outstanding, basic (in shares)	63,728,393	63,034,185	63,545,065	62,868,745
Dilutive shares (in shares)	206,493	164,114	182,658	160,644
Weighted average common shares outstanding, diluted (in shares)	63,934,886	63,198,299	63,727,723	63,029,389
Income available to common stockholders, per share amount, basic (usd per share)	$ 0.36	$ 0.33	$ 1.03	$ 0.99
Income available to common stockholders, per share amount, diluted (usd per share)	$ 0.36	$ 0.33	$ 1.02	$ 0.99