Summary of Significant Accounting Policies (Reconciliation of Numerators and Denominators of Basic and Diluted Earnings Per Share Calculations) (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Accounting Policies [Abstract]
Net income	$ 19,802	$ 17,029
Income available to common stockholders, Basic	19,802	17,029
Income available to common stockholders, Diluted	$ 19,802	$ 17,029
Weighted average basic shares outstanding, Basic	62,673,887	57,369,039
Weighted average basic shares outstanding, Diluted	167,064	159,380
Weighted average common shares outstanding, Diluted	62,840,951	57,528,419
Income available to common stockholders, per share amount, Basic	$ 0.32	$ 0.30
Income available to common stockholders, per share amount, Diluted	$ 0.32	$ 0.30