Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Activities:
Net Income	$ 86,830	$ 62,121	$ 56,808
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	6,500	6,100	11,000
Gains on sales of loans	(6,354)	(4,451)	(7,108)
Proceeds from sales of loans	228,995	153,743	218,237
Loans originated for sale	(220,765)	(150,795)	(198,683)
Gain on sale of investment securities	(630)	0	(1,133)
Net gains from sales/writedowns of other real estate and repossessed assets	(2,681)	(1,886)	(2,943)
Depreciation of premises and equipment	11,028	8,980	8,713
Amortization and impairment of intangible assets	8,244	3,545	3,492
Net amortization of premiums and discounts on investment securities	6,007	4,497	4,196
Share-based compensation expense	3,478	2,931	2,854
Deferred income tax	5,700	(1,700)	635
Contributions to defined benefit pension plan	0	0	(15,000)
Net (increase) decrease in interest receivable and other assets	(20,570)	953	6,197
Net increase (decrease) in interest payable and other liabilities	(2,800)	5,893	2,414
Net Cash Provided by Operating Activities	102,982	89,931	89,679
Investment securities — available-for-sale:
Proceeds from maturities, calls and principal reductions	239,179	165,749	154,959
Proceeds from sales and redemptions	13,173	0	38,028
Purchases	0	0	(304,264)
Investment securities — held-to-maturity:
Proceeds from maturities, calls and principal reductions	87,189	83,989	65,790
Purchases	(279,226)	(127,187)	(109,655)
Net increase in loans	(493,776)	(586,121)	(502,687)
Proceeds from sales of other real estate and repossessed assets	16,720	12,486	18,018
Purchases of premises and equipment, net	(8,527)	(13,411)	(8,664)
Payments to Acquire Businesses, Net of Cash Acquired	16,551	(14,260)	0
Net Cash Used in Investing Activities	(408,717)	(478,755)	(648,475)
Financing Activities
Net increase in interest- and noninterest-bearing demand deposits and savings accounts	479,386	277,781	341,568
Net decrease in time deposits	(170,598)	(115,642)	(140,626)
Net increase (decrease) in short-term borrowings	(31,268)	62,039	16,965
Proceeds from (Repayments of) Other Debt	125,000	0	0
Repayments of Other Debt	6,000	10,310	34,289
Cash dividends paid	(36,918)	(29,528)	(24,521)
Proceeds from issuance of common stock, net of issuance costs	0	76,175	53,925
Proceeds from directors' stock purchase plan and exercise of stock options	2,473	1,242	806
Cash paid for payroll taxes upon conversion of restricted stock units	(571)	(701)	(379)
Net Cash Provided by Financing Activities	361,504	261,056	213,449
Net Increase (Decrease) in Cash and Cash Equivalents	55,769	(127,768)	(345,347)
Cash and Cash Equivalents at Beginning of Year	183,020	310,788	656,135
Cash and Cash Equivalents at End of Year	238,789	183,020	310,788
Supplemental Disclosure of Cash Flow Information:
Interest paid	16,958	14,823	18,047
Federal income taxes paid	41,450	25,900	19,150
Loans transferred to other real estate and repossessed assets	9,329	11,308	6,382
Closed branch offices transferred to other real estate	2,692	841	382
Business combinations:
Fair value of tangible assets acquired (noncash)	1,282,420	747,181	0
Goodwill and identifiable intangible assets acquired	118,744	82,090	0
Liabilities assumed	1,258,051	815,011	0
Shares and Stock Options Issued in Acquisition	$ 159,904	$ 0	$ 0