Quarterly Financial Data (Unaudited) (Details) (USD $) In Thousands, except Share data, 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
Quarterly Financial Information Disclosure [Abstract]
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	84,378	82,548	80,414	76,894	76,107	75,308	78,910	74,353	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
Net interest income after provision for credit losses	84,378	82,548	80,414	76,894	76,107	73,308	74,910	70,353	324,234	294,678	265,195
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
Income tax expense (benefit)	(6,980)	(8,056)	(12,978)	(9,853)	3,201	0	288,842	0	(37,867)	292,043	0
Net income	$ 22,154	$ 21,048	$ 27,761	$ 22,678	$ 20,946	$ 30,598	$ 320,886	$ 13,291
Earnings per share - basic (in dollars per share)	$ 0.36	$ 0.34	$ 0.45	$ 0.36	$ 0.34	$ 0.49	$ 5.17	$ 0.21	$ 1.50	$ 6.21	$ 0.63
Earnings per share - diluted (in dollars per share)	$ 0.35	$ 0.33	$ 0.44	$ 0.36	$ 0.33	$ 0.49	$ 5.13	$ 0.21	$ 1.48	$ 6.14	$ 0.63
Weighted average shares outstanding - basic (in shares)	62,319,497	62,309,270	62,289,437	62,242,183	62,159,683	62,139,833	62,112,936	62,078,404	62,290,361	62,122,862	61,955,659
Weighted average shares outstanding - diluted (in shares)	63,613,271	63,461,018	63,107,913	63,004,784	62,867,030	62,845,864	62,610,054	62,682,987	63,371,763	62,772,079	62,231,208