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
	Mar. 31, 2017	Mar. 31, 2016
Accounting Policies [Abstract]
Net income	$ 23,508	$ 20,973
Income available to common stockholders, basic	23,508	20,973
Income available to common stockholders, diluted	$ 23,508	$ 20,973
Weighted average common shares outstanding, basic (in shares)	64,167,376	63,351,093
Dilutive shares (in shares)	202,229	168,662
Weighted average common shares outstanding, diluted (in shares)	64,369,605	63,519,755
Income available to common stockholders, per share amount, basic (usd per share)	$ 0.37	$ 0.33
Income available to common stockholders, per share amount, diluted (usd per share)	$ 0.37	$ 0.33