Segment Reporting (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Segment Income Statement Data Abstract
Net interest income	$ 157,653	$ 154,668
Noninterest income	82,000	78,446
Total revenue	239,653	233,114
Credit provision	4,000	0
Noninterest expense	166,915	169,762
Income before income taxes	68,738	63,352
Income tax expense	21,350	20,719
Net income	47,388	42,633
Return on average allocated capital	10.10%	9.20%
Segment Balance Sheet Data
Average earning assets	20,680,919	19,371,729
Average loans	15,448,152	14,310,441
Average deposits	17,146,384	15,000,567
Average allocated capital	1,856,431	1,801,649
Commercial Banking Segment [Member]
Segment Income Statement Data Abstract
Net interest income	77,184	71,373
Noninterest income	23,169	19,641
Total revenue	100,353	91,014
Credit provision	12,435	10,925
Noninterest expense	46,747	47,818
Income before income taxes	41,171	32,271
Income tax expense	14,410	11,295
Net income	26,761	20,976
Return on average allocated capital	14.40%	11.90%
Segment Balance Sheet Data
Average earning assets	8,156,150	6,996,753
Average loans	8,145,829	6,993,699
Average deposits	5,374,633	4,278,618
Average allocated capital	754,399	709,873
Consumer Banking Segment [Member]
Segment Income Statement Data Abstract
Net interest income	79,262	79,534
Noninterest income	54,195	53,094
Total revenue	133,457	132,628
Credit provision	4,944	4,873
Noninterest expense	110,438	106,698
Income before income taxes	18,075	21,057
Income tax expense	6,326	7,370
Net income	11,749	13,687
Return on average allocated capital	8.60%	9.80%
Segment Balance Sheet Data
Average earning assets	7,298,554	7,297,135
Average loans	7,298,554	7,297,135
Average deposits	9,598,352	9,506,024
Average allocated capital	554,672	561,397
Other Segment [Member]
Segment Income Statement Data Abstract
Net interest income	1,207	3,761
Noninterest income	4,636	5,711
Total revenue	5,843	9,472
Credit provision	(13,379)	(15,798)
Noninterest expense	9,730	15,246
Income before income taxes	9,492	10,024
Income tax expense	614	2,054
Net income	8,878	7,970
Return on average allocated capital	5.60%	5.10%
Segment Balance Sheet Data
Average earning assets	5,226,215	5,077,841
Average loans	3,769	19,607
Average deposits	2,173,399	1,215,925
Average allocated capital	$ 547,360	$ 530,379