Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating Activities:
Net Income	$ 56,808	$ 51,008	$ 43,050
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	11,000	18,500	26,000
Gains on sales of loans	(7,108)	(9,645)	(5,017)
Proceeds from sales of loans	218,237	314,521	224,341
Loans originated for sale	(198,683)	(303,723)	(217,663)
Gain on sale of investment securities	(1,133)	(34)	0
Net gains on sales of other real estate and repossessed assets	(2,943)	(1,532)	(2,208)
Net (gain) loss on disposal of premises and equipment and branch bank properties	(281)	0	616
Depreciation of premises and equipment	8,713	8,142	7,950
Amortization of intangible assets	3,492	3,969	3,615
Net amortization of premiums and discounts on investment securities	4,196	4,795	4,024
Share-based compensation expense	2,854	1,865	1,517
Deferred income tax	635	12,668	6,413
Contributions to defined benefit pension plan	(15,000)	(12,000)	0
Net decrease in interest receivable and other assets	6,478	4,295	10,747
Net increase (decrease) in interest payable and other liabilities	2,414	2,337	(909)
Net Cash Provided by Operating Activities	89,679	95,166	102,476
Investment securities — available-for-sale:
Proceeds from maturities, calls and principal reductions	154,959	268,848	327,013
Proceeds from sales and redemptions	38,028	0	0
Purchases	(304,264)	(191,689)	(419,714)
Investment securities — held-to-maturity:
Proceeds from maturities, calls and principal reductions	65,790	55,352	52,115
Purchases	(109,655)	(102,034)	(70,014)
Net increase in loans	(502,687)	(330,760)	(196,484)
Proceeds from sales of other real estate and repossessed assets	18,018	24,341	19,202
Purchases of premises and equipment, net	(8,664)	(10,303)	(8,602)
Purchase of bank owned life insurance	0	0	(3,600)
Cash acquired, net of cash paid, in business combinations	0	339,372	0
Net Cash Provided by (Used in) Investing Activities	(648,475)	53,127	(300,084)
Financing Activities
Net increase in interest- and noninterest-bearing demand deposits and savings accounts	341,568	307,972	113,164
Net decrease in time deposits	(140,626)	(157,425)	(78,072)
Net increase in short-term borrowings	16,965	6,677	61,083
Repayment of FHLB advances	(34,289)	(8,768)	(31,073)
Cash dividends paid	(24,521)	(22,566)	(21,964)
Proceeds from Issuance of Common Stock	53,925	0	0
Proceeds from directors' stock purchase plan and exercise of stock options	806	260	245
Cash paid for payroll taxes upon conversion of restricted stock units	(379)	(248)	0
Net Cash Provided by Financing Activities	213,449	125,902	43,383
Net Increase (Decrease) in Cash and Cash Equivalents	(345,347)	274,195	(154,225)
Cash and Cash Equivalents at Beginning of Year	656,135	381,940	536,165
Cash and Cash Equivalents at End of Year	310,788	656,135	381,940
Supplemental Disclosure of Cash Flow Information:
Interest paid	18,047	23,859	32,129
Federal income taxes paid	19,150	9,029	7,787
Loans transferred to other real estate and repossessed assets	6,382	15,794	19,664
Closed branch offices transferred to other real estate	382	0	0
Business combinations:
Fair value of tangible assets acquired (noncash)	0	52,337	0
Goodwill and identifiable intangible assets acquired	0	12,350	0
Liabilities assumed	$ 0	$ 404,059	$ 0