Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 215,632	$ 149,296	$ 131,461
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	28,142	28,363	28,763
Provision for loan losses	58,968	110,659	73,038
(Gain) loss on other real estate owned	(2,839)	(4,444)	635
Deferred tax (benefit) expense	49,831	(7,839)	16,685
Increase in cash surrender value of life insurance contracts	(14,959)	(11,112)	(9,789)
Gain on the sale of loans	(3,363)	(4,414)
(Gain) loss on disposal of other assets	1,587	(5,180)	1,815
Net (increase) decrease in loans held for sale	3,317	(14,267)	(289)
Net amortization of securities premium/discount	33,244	29,048	21,105
Amortization of intangible assets	22,417	19,781	24,184
Amortization of FDIC indemnification assets	2,427	5,918	5,747
Stock-based compensation expense	17,633	14,266	12,944
Increase (decrease) in interest payable and other liabilities	2,307	10,315	(4,722)
Net payments (to) from FDIC for loss share claims	2,299	(3,134)	14,051
Decrease in FDIC loss share receivable	8,613	5,667	6,407
(Increase) decrease in other assets	(9,836)	15,197	(94,816)
Other, net	(4,335)	5,795	8,511
Net cash provided by operating activities	411,085	343,915	235,730
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from sales of securities available for sale	213,877	173,215	9,289
Proceeds from maturities of securities available for sale	338,843	408,311	842,114
Purchases of securities available for sale	(742,279)	(1,071,869)	(1,323,853)
Proceeds from maturities of securities held to maturity	373,088	425,453	538,777
Purchases of securities held to maturity	(863,457)	(563,661)	(749,102)
Net (increase) decrease in short-term investments	351,087	487,378	237,393
Proceeds from sale of loans	59,483	177,645	3,533
Net increase in loans	(1,051,628)	(1,331,125)	(1,868,548)
Purchase of life insurance contracts	(50,000)	(40,000)
Purchases of property and equipment	(20,297)	(19,272)	(23,804)
Proceeds from sales of property and equipment	1,853	7,445	14,259
Proceeds from sales of other real estate	24,324	24,624	47,115
Cash received in excess of cash paid for acquisitions	476,609
Other, net	(6,824)	825	(3,604)
Net cash used in investing activities	(895,321)	(1,321,031)	(2,276,431)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net increase in deposits	900,427	1,075,370	1,776,081
Net increase (decrease) in short-term borrowings	(118,151)	(198,238)	272,071
Repayments of long-term debt	(204,111)	(21,271)	(157,933)
Issuance of long-term debt	165	6,838	273,565
Dividends paid	(83,266)	(76,551)	(77,013)
Payroll tax remitted on net share settlement of equity awards	(11,881)	(3,178)	(3,385)
Repurchase of common stock			(95,613)
Proceeds from exercise of stock options	12,092	2,147	347
Proceeds from issuance of common stock in public offering		259,299
Proceeds from dividend reinvestment and stock purchase plan	3,220	1,515
Net cash provided by financing activities	498,495	1,045,931	1,988,120
NET INCREASE (DECREASE) IN CASH AND DUE FROM BANKS	14,259	68,815	(52,581)
CASH AND DUE FROM BANKS, BEGINNING	372,689	303,874	356,455
CASH AND DUE FROM BANKS, ENDING	386,948	372,689	303,874
SUPPLEMENTAL INFORMATION
Income taxes paid	45,092	30,184	31,896
Interest paid	108,702	69,624	51,201
SUPPLEMENTAL INFORMATION FOR NON-CASH INVESTING AND FINANCING ACTIVITIES
Assets acquired in settlement of loans	$ 19,140	$ 16,314	$ 15,462