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, 2014	Mar. 31, 2013
Accounting Policies [Abstract]
Net income	$ 17,029	$ 17,828
Income available to common stockholders, Basic	17,029	17,828
Income available to common stockholders, Diluted	$ 17,029	$ 17,828
Weighted Average Common Shares Outstanding, Basic	57,369,039	57,167,198
Dilutive shares	159,380	170,017
Weighted Average Common Shares Outstanding, Diluted	57,528,419	57,337,215
Income available to common stockholders, Per Share Amount, Basic	$ 0.30	$ 0.31
Income available to common stockholders, Per Share Amount, Diluted	$ 0.30	$ 0.31