Consolidated Statements of Cash Flows (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating activities
Net income	$ 75,074,000	$ 61,747,000	$ 54,558,000
Adjustments to reconcile net income to net cash provided by operating activities
Provision for loan and lease losses	19,539,000	22,424,000	20,269,000
Depreciation and amortization of premises and equipment	8,324,000	7,948,000	6,276,000
Net accretion on securities	3,216,000	5,058,000	2,408,000
Amortization of intangible assets	5,047,000	4,872,000	3,394,000
Stock based compensation	3,521,000	4,305,000	4,364,000
Bank owned life insurance income	(5,349,000)	(3,793,000)	(3,077,000)
Trading security purchases	(1,626,000)	(1,085,000)	(753,000)
Unrealized (gains) losses in trading securities	(388,000)	(776,000)	(103,000)
Deferred income tax benefit	8,347,000	2,344,000	(10,000)
Proceeds from sale of loans held for sale	7,050,000	71,342,000	65,160,000
Originations and purchases of loans held for sale	(10,215,000)	(66,512,000)	(66,252,000)
Net gains on sales of loans held for sale	(17,000)	(1,288,000)	(2,469,000)
Net security gains	(92,000)	(1,426,000)	(599,000)
Net gains on sales of other real estate owned	(459,000)	(1,106,000)	(988,000)
Gain on sale of equity investment	(19,401,000)	0	0
Prepayment penalties on long-term debt	17,903,000	0	0
Net decrease (increase) in other assets	(27,949,000)	20,463,000	6,804,000
Net (decrease) increase in other liabilities	5,286,000	(5,219,000)	(128,000)
Net cash provided by operating activities	87,811,000	119,298,000	88,854,000
Investing activities
Net cash provided by acquisitions	0	80,883,000	52,871,000
Securities available for sale:
Proceeds from maturities, calls, and principal paydowns	236,133,000	376,509,000	573,828,000
Proceeds from sales	189,000	27,593,000	1,790,000
Purchases	(197,652,000)	(353,714,000)	(483,858,000)
Securities held to maturity:
Proceeds from maturities, calls, and principal paydowns	44,756,000	34,413,000	31,506,000
Purchases	(49,479,000)	(84,621,000)	(20,193,000)
Other:
Net increase in loans	(212,238,000)	(255,318,000)	(277,530,000)
Proceeds from FHLB stock redemption	78,441,000	27,409,000	0
Purchases of Federal Reserve and FHLB stock	(64,203,000)	(36,366,000)	(1,886,000)
Proceeds from bank owned life insurance	6,064,000	0	0
Purchases of premises and equipment, net	(9,003,000)	(5,766,000)	(6,994,000)
Proceeds from sales of equity investment	19,639,000	0	0
Proceeds from sales of other real estate owned	3,612,000	5,224,000	3,616,000
Net cash used in investing activities	(143,741,000)	(183,754,000)	(126,850,000)
Financing activities
Net (decrease) increase in deposits	409,381,000	(7,545,000)	135,095,000
Net increase (decrease) in short-term borrowings	(139,240,000)	271,497,000	(18,651,000)
Proceeds from issuance of long-term debt	120,051,000	0	0
Repayments of long-term debt	(315,831,000)	(163,595,000)	(3,354,000)
Proceeds from the issuance of shares to employee benefit plans and other stock plans	6,256,000	5,334,000	1,395,000
Purchase of treasury stock	(72,000)	(12,459,000)	(15,490,000)
Cash dividends and payment for fractional shares	(36,905,000)	(33,518,000)	(26,712,000)
Net cash provided by financing activities	43,640,000	59,714,000	72,283,000
Net (decrease) increase in cash and cash equivalents	(12,290,000)	(4,742,000)	34,287,000
Cash and cash equivalents at beginning of year	158,926,000	163,668,000	129,381,000
Cash and cash equivalents at end of year	146,636,000	158,926,000	163,668,000
Cash paid during the period for:
Interest	23,387,000	31,307,000	35,344,000
Income taxes, net of refund	38,912,000	20,848,000	25,512,000
Noncash investing activities:
Loans transferred to other real estate owned	4,330,000	4,746,000	2,734,000
Preferred stock acquired from sale of equity investment	2,762,000	0	0
Transfer of available for sale securities to held to maturity portfolio	332,115,000	0	0
Acquisitions:
Fair value of assets acquired	0	1,505,490,000	258,467,000
Fair value of liabilities assumed	0	1,285,718,000	285,012,000
Fair value of debt issued in purchase combination	$ 0	$ 0	$ 502,000