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		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Accounting Policies [Abstract]
Net income	$ 21,356	$ 21,796	$ 42,329	$ 41,598
Income available to common stockholders, basic	21,356	21,796	42,329	41,598
Income available to common stockholders, diluted	$ 21,356	$ 21,796	$ 42,329	$ 41,598
Weighted average common shares outstanding, basic (in shares)	63,553,694	62,894,213	63,452,393	62,784,655
Dilutive shares (in shares)	172,819	150,752	170,741	158,908
Weighted average common shares outstanding, diluted (in shares)	63,726,513	63,044,965	63,623,134	62,943,563
Income available to common stockholders, per share amount, basic (usd per share)	$ 0.34	$ 0.35	$ 0.67	$ 0.66
Income available to common stockholders, per share amount, diluted (in shares)	$ 0.34	$ 0.35	$ 0.67	$ 0.66