Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net income	$ 116,172	$ 131,961	$ 143,627
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	19,465	19,712	18,477
Stock-based compensation	7,489	6,055	4,816
Provision for credit losses	1,884	16,095	25,552
Net amortization of premiums and accretion of discounts on securities and borrowings	26,949	16,229	21,124
Amortization of other intangible assets	9,919	8,258	9,783
Gains on securities transactions, net	(745)	(14,678)	(2,587)
Net impairment losses on securities recognized in earnings	0	0	5,247
Proceeds from sales of loans held for sale	85,452	1,083,297	999,380
Gains on sales of loans, net	(1,731)	(33,695)	(46,998)
Originations of loans held for sale	(91,463)	(953,125)	(923,182)
(Gains) losses on sales of assets, net	(18,087)	(10,947)	329
Net deferred income tax expense	11,455	30,329	28,398
FDIC loss-share receivable (excluding reimbursements)	20,792	8,427	7,459
Net change in:
Trading securities	31	7,893	(219)
Fair value of borrowings carried at fair value	0	(881)	(2,574)
Cash surrender value of bank owned life insurance	(6,392)	(5,962)	(6,855)
Accrued interest receivable	423	(1,589)	5,446
Other assets	17,231	(17,587)	49,345
Accrued expenses and other liabilities	(14,868)	(4,428)	(13,257)
Net cash provided by operating activities	183,976	285,364	323,311
Cash flows from investing activities:
Net loan originations	(649,616)	(368,724)	(203,354)
Loans purchased	(128,684)	(231,008)	(136,241)
Investment securities held to maturity:
Purchases	(397,186)	(619,299)	(360,614)
Maturities, calls and principal repayments	347,531	473,362	705,487
Investment securities available for sale:
Purchases	(28,415)	(289,181)	(455,601)
Sales	62,025	57,003	257,497
Maturities, calls and principal repayments	153,673	183,006	248,721
Death benefit proceeds from bank owned life insurance	0	1,821	1,689
Proceeds from sales of real estate property and equipment	43,360	18,034	9,337
Purchases of real estate property and equipment	(21,862)	(14,852)	(22,735)
(Payments to) reimbursements from the FDIC	5,582	3,812	21,935
Cash and cash equivalents acquired in acquisitions	102,025	0	117,587
Net cash (used in) provided by investing activities	(511,567)	(786,026)	183,708
Cash flows from financing activities:
Net change in deposits	1,300,011	55,244	210,623
Net change in short-term borrowings	(151,470)	127,132	(87,526)
Issuance of long-term borrowings	0	125,000	0
Repayments of long-term borrowings	(275,000)	(26,133)	(28,000)
Redemption of junior subordinated debentures	0	(142,313)	(10,000)
Cash dividends paid to common shareholders	(88,119)	(129,271)	(125,870)
Common stock issued, net	3,408	7,071	7,805
Net cash provided by (used in) financing activities	788,830	16,730	(32,968)
Net change in cash and cash equivalents	461,239	(483,932)	474,051
Cash and cash equivalents at beginning of year	369,168	853,100	379,049
Cash and cash equivalents at end of year	830,407	369,168	853,100
Supplemental disclosures of cash flow information:
Interest on deposits and borrowings	162,762	167,860	183,120
Federal and state income taxes	34,236	15,317	50,111
Supplemental schedule of non-cash investing activities:
Transfer of loans to other real estate owned	11,012	19,679	14,365
Loans transferred to loans held for sale	27,329	0	124,261
Non-cash assets acquired:
Loans	1,160,852	0	1,088,421
Premises and equipment, net	11,234	0	9,457
Bank owned life insurance	25,224	0	0
Accrued interest receivable	3,792	0	5,294
FDIC loss-share receivable	7,465	0	0
Goodwill	147,658	0	109,758
Other intangible assets, net	11,500	0	8,050
Other assets	42,876	0	72,137
Total non-cash assets acquired	1,634,605	0	1,568,767
Liabilities assumed:
Deposits	1,414,843	0	1,380,293
Short-term borrowings	16,796	0	29,000
Junior subordinated debentures issued to capital trusts	0	0	15,645
Accrued expenses and other liabilities	13,768	0	52,998
Total liabilities assumed	1,445,407	0	1,477,936
Net non-cash assets acquired	189,198	0	90,831
Net cash and cash equivalents acquired in acquisition	102,025	0	117,587
Common stock issued in acquisition	291,223	0	208,418
Held-to-maturity Securities [Member]
Non-cash assets acquired:
Investments securities held to maturity	7,930	0	0
Available for sale securities [Member]
Non-cash assets acquired:
Investments securities held to maturity	$ 216,074	$ 0	$ 275,650