Earnings Per Common Share - Calculation of Both Basic and Diluted Earnings Per Common Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Earnings Per Share [Abstract]
Net income	$ 33,922	$ 32,820	$ 65,232	$ 67,351
Basic weighted-average number of common shares outstanding	199,244,243	197,246,322	199,085,501	197,088,528
Plus: Common stock equivalents		3,846		17,110
Diluted weighted-average number of common shares outstanding	199,244,243	197,250,168	199,085,501	197,105,638
Earnings per common share:
Basic	$ 0.17	$ 0.17	$ 0.33	$ 0.34
Diluted	$ 0.17	$ 0.17	$ 0.33	$ 0.34