Summary of Significant Accounting Policies - Summary of Effects of Adjustment on Amounts Previously Reported in Consolidated Financial Statements and Corrected Amounts (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Other assets	$ 538,495				$ 594,382								$ 538,495	$ 594,382
Accrued expenses and other liabilities	202,784				194,368								202,784	194,368
Retained earnings	93,495				78,599								93,495	78,599
Net occupancy and equipment expense													71,245	66,332	63,771
Income tax expense (benefit)	14,702	22,402	14,366	15,278	7,321	[1]	13,489	[1]	24,999	[1]	16,897	[1]	66,748	62,706	54,929
Net income	36,829	39,447	32,820	34,531	24,532	[1]	35,072	[1]	36,608	[1]	36,299	[1]	143,627	132,511	130,006
Earnings Per Common Share:
Basic	$ 0.19	$ 0.20	$ 0.17	$ 0.18	$ 0.14		$ 0.20		$ 0.21		$ 0.20		$ 0.73	$ 0.74	$ 0.73
Diluted	$ 0.19	$ 0.20	$ 0.17	$ 0.18	$ 0.14		$ 0.20		$ 0.21		$ 0.20		$ 0.73	$ 0.74	$ 0.73
As Reported [Member]
Other assets					586,134									586,134
Accrued expenses and other liabilities					174,708									174,708
Retained earnings					90,011									90,011
Net occupancy and equipment expense														64,364	61,765
Income tax expense (benefit)														63,532	55,771
Net income														133,653	131,170
Earnings Per Common Share:
Basic														$ 0.75	$ 0.74
Diluted														$ 0.75	$ 0.74
Adjustment [Member]
Other assets					8,248									8,248
Accrued expenses and other liabilities					19,660									19,660
Retained earnings					(11,412)									(11,412)
Net occupancy and equipment expense														1,968	2,006
Income tax expense (benefit)														(826)	(842)
Net income														(1,142)	(1,164)
Earnings Per Common Share:
Basic														$ (0.01)	$ (0.01)
Diluted														$ (0.01)	$ (0.01)
As Adjusted [Member]
Other assets					594,382									594,382
Accrued expenses and other liabilities					194,368									194,368
Retained earnings					78,599									78,599
Net occupancy and equipment expense														66,332	63,771
Income tax expense (benefit)														62,706	54,929
Net income														$ 132,511	$ 130,006
Earnings Per Common Share:
Basic														$ 0.74	$ 0.73
Diluted														$ 0.74	$ 0.73

[1] Previously reported amounts have been revised to reflect an increase in non-interest expense due to the immaterial correction of an error. See the "Correction of an Immaterial Error" section of Note 1 to the consolidated financial statements for additional information.