Summary of Significant Accounting Policies - Calculation of Both Basic and Diluted Earnings Per Common Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Earnings Per Share [Abstract]
Net income	$ 39,608	$ 27,121	$ 33,922	$ 31,310	$ 36,829	$ 39,447	$ 32,820	$ 34,531	$ 131,961	$ 143,627	$ 132,511
Basic weighted-average number of common shares outstanding	199,613,524	199,445,874	199,244,243	198,924,995	197,795,817	197,437,988	197,246,322	196,930,733	199,309,425	197,354,159	178,424,883
Plus: Common stock equivalents										213	1,187
Diluted weighted-average number of common shares outstanding	199,613,524	199,445,874	199,244,243	198,924,995	197,795,817	197,437,988	197,250,168	196,961,915	199,309,425	197,354,372	178,426,070
Earnings per common share:
Basic	$ 0.20	$ 0.14	$ 0.17	$ 0.16	$ 0.19	$ 0.20	$ 0.17	$ 0.18	$ 0.66	$ 0.73	$ 0.74
Diluted	$ 0.20	$ 0.14	$ 0.17	$ 0.16	$ 0.19	$ 0.20	$ 0.17	$ 0.18	$ 0.66	$ 0.73	$ 0.74