CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating activities:
Net income	$ 91,353	$ 78,829	$ 77,068
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	13,082	12,236	11,482
Amortization of intangible assets	4,287	4,469	4,607
Net accretion/amortization on securities, loans and borrowings	(3,533)	(5,959)	(9,379)
Stock-based compensation	3,993	3,961	3,668
Provision for loan losses	7,178	7,992	9,108
Provision for deferred income taxes	7,461	7,130	12,032
Amortization of mortgage servicing rights	444	529	687
Income from bank-owned life insurance policies	(1,037)	(1,066)	(1,121)
Gain on sales of investment securities, net	0	(80,768)	(291)
Loss on debt extinguishments	0	87,336	0
Net (gain) loss on sale of loans and other assets	(154)	257	247
Net change in loans originated for sale	137	(515)	608
Change in other assets and liabilities	(10)	(11,247)	(292)
Net cash provided by operating activities	123,201	103,184	108,424
Investing activities:
Proceeds from sales of available-for-sale investment securities	0	713,694	5,378
Proceeds from sales of held-to-maturity investment securities	0	450,032	0
Proceeds from maturities of available-for-sale investment securities	137,282	234,021	215,223
Proceeds from maturities of held-to-maturity investment securities	0	31,595	28,340
Proceeds from maturities of other securities	13	26,649	278
Purchases of available-for-sale investment securities	(310,517)	(923,588)	(752,891)
Purchases of held-to-maturity investment securities	0	(8,308)	(110,925)
Purchases of other securities	(7,500)	0	(615)
Net change in loans	(137,207)	(248,962)	(239,174)
Cash received for acquisitions, net of cash acquired of $0, $291,990, and $5,510, respectively	(924)	291,980	600,972
Purchases of premises and equipment, net	(13,376)	(13,855)	(10,846)
Net cash (used in)/provided by investing activities	(332,229)	553,258	(264,260)
Financing activities:
Net change in deposits	39,220	(35,451)	34,832
Net change in borrowings, net of payments of $13, $815,384 and $220	196,087	(673,484)	(220)
Issuance of common stock	9,989	15,239	64,145
Purchases of treasury stock	(4,368)	0	0
Sales of treasury stock	959	0	0
Cash dividends paid	(46,178)	(43,482)	(40,765)
Tax benefits from share-based payment arrangements	2,068	1,825	1,524
Net cash provided by/(used in) financing activities	197,777	(735,353)	59,516
Change in cash and cash equivalents	(11,251)	(78,911)	(96,320)
Cash and cash equivalents at beginning of year	149,647	228,558	324,878
Cash and cash equivalents at end of year	138,396	149,647	228,558
Supplemental disclosures of cash flow information:
Cash paid for interest	11,937	30,141	51,541
Cash paid for income taxes	29,457	23,648	16,462
Supplemental disclosures of noncash financing and investing activities:
Dividends declared and unpaid	12,254	11,332	10,699
Transfers from loans to other real estate	2,546	8,325	5,059
Transfer of investment securities from held-to-maturity to available-for-sale	0	198,890	0
Acquisitions:
Fair value of assets acquired, excluding acquired cash and intangibles	164	3,678	165,885
Fair value of liabilities assumed	$ 0	$ 303,494	$ 798,031