Segment Information (Summarized Financial Information Concerning Segments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Segment Reporting Information [Line Items]
Net interest income	$ 76,595	$ 72,592	$ 62,319	$ 61,367	$ 53,977	$ 54,168	$ 55,154	$ 55,117	$ 272,873	$ 218,416	$ 231,399
Provision for loan losses	1,036	(82)	3,207	3,312	7,100	6,400	8,000	9,281	7,473	30,781	63,280
Noninterest income	49,147	47,326	43,589	42,821	42,205	41,979	42,974	42,992	182,883	170,150	163,460
Noninterest expense	93,680	95,158	79,758	79,925	83,272	76,102	77,871	77,060	348,521	314,305	338,956
Income (loss) before income taxes	31,026	24,842	22,943	20,951	5,810	13,645	12,257	11,768	99,762	43,480	(7,377)
Total assets	8,609,683				7,263,892				8,609,683	7,263,892	8,005,335
Community Banking [Member]
Segment Reporting Information [Line Items]
Net interest income									302,285	252,519	287,404
Provision for loan losses									5,912	30,806	63,284
Noninterest income									120,170	88,037	94,132
Noninterest expense									287,097	236,642	270,249
Income (loss) before income taxes									129,446	73,108	48,003
Total assets	5,035,431				3,759,529				5,035,431	3,759,529	4,487,007
Treasury [Member]
Segment Reporting Information [Line Items]
Net interest income									(42,393)	(30,378)	(47,490)
Provision for loan losses									0	0	126
Noninterest income									13,235	17,871	5,422
Noninterest expense									747	13,803	7,878
Income (loss) before income taxes									(29,905)	(26,310)	(50,072)
Total assets	3,377,568				3,396,189				3,377,568	3,396,189	3,401,958
Other [Member]
Segment Reporting Information [Line Items]
Net interest income									12,981	(3,725)	(8,515)
Provision for loan losses									1,561	(25)	(130)
Noninterest income									49,478	64,242	63,906
Noninterest expense									60,677	63,860	60,829
Income (loss) before income taxes									221	(3,318)	(5,308)
Total assets	$ 196,684				$ 108,174				$ 196,684	$ 108,174	$ 116,370