Segment Information (Details) (USD $) In Thousands, 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
Segment Reporting Information [Line Items]
Interest income	$ 97,803	$ 96,444	$ 94,017	$ 90,757	$ 94,254	$ 95,991	$ 100,990	$ 97,965	$ 379,021	$ 389,200	$ 404,292
Interest expense	13,425	13,896	13,603	13,863	18,147	20,683	22,080	23,612	54,787	84,522	109,097
Net interest income									324,234	304,678	295,195
Provision for credit losses	0	0	0	0	0	2,000	4,000	4,000	0	10,000	30,000
Noninterest Income	29,127	31,890	42,003	37,566	31,227	46,698	44,741	31,587	140,586	154,253	126,328
Noninterest expense	84,371	85,334	81,678	81,929	89,589	89,408	87,607	88,649	333,312	355,253	352,390
Income before income taxes	29,134	29,104	40,739	32,531	17,745	30,598	32,044	13,291	131,508	93,678	39,133
Total assets	10,319,249				9,236,910				10,319,249	9,236,910	9,193,237
Community Banking
Segment Reporting Information [Line Items]
Interest income									352,907	360,901	387,365
Interest expense									49,634	78,004	102,963
Net interest income									303,273	282,897	284,402
Provision for credit losses									0	9,980	56,507
Noninterest Income									73,380	46,433	76,337
Noninterest expense									246,185	266,486	295,139
Income before income taxes									130,468	52,864	9,093
Total assets	10,147,510				8,754,170				10,147,510	8,754,170	9,219,398
Home Loan Division
Segment Reporting Information [Line Items]
Interest income									26,114	28,299	16,927
Interest expense									0	0	0
Net interest income									26,114	28,299	16,927
Provision for credit losses									0	20	71
Noninterest Income									67,670	108,391	48,865
Noninterest expense									80,592	92,742	58,979
Income before income taxes									13,192	43,928	6,742
Total assets	144,403				477,127				144,403	477,127	2,594
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Interest income									0	0	0
Interest expense									5,153	6,518	6,134
Net interest income									(5,153)	(6,518)	(6,134)
Provision for credit losses									0	0	(26,578)
Noninterest Income									(464)	(571)	1,126
Noninterest expense									6,535	(3,975)	(1,728)
Income before income taxes									(12,152)	(3,114)	23,298
Total assets	$ 27,336				$ 5,613				$ 27,336	$ 5,613	$ (28,755)