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, 2016	Mar. 31, 2015
Accounting Policies [Abstract]
Net income	$ 20,973	$ 19,802
Income available to common stockholders, basic	20,973	19,802
Income available to common stockholders, diluted	$ 20,973	$ 19,802
Weighted average common shares outstanding, basic (in shares)	63,351,093	62,673,887
Dilutive shares (in shares)	168,662	167,064
Weighted average common shares outstanding, diluted (in shares)	63,519,755	62,840,951
Income available to common stockholders, per share amount, basic (usd per share)	$ 0.33	$ 0.32
Income available to common stockholders, per share amount, diluted (in shares)	$ 0.33	$ 0.32