CONSOLIDATED STATEMENTS OF CASH FLOW - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Cash Flows [Abstract]
Net income	$ 82,414	$ 68,051	$ 57,786
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan and lease losses	19,462	8,980	5,833
Depreciation of premises and equipment	5,620	5,658	5,245
Depreciation of equipment owned and leased to others	26,248	25,215	21,678
Stock-based compensation	3,553	2,963	2,884
Amortization of investment securities premiums and accretion of discounts, net	3,477	5,449	5,861
Amortization of mortgage servicing rights	956	1,092	1,478
Deferred income taxes	(550)	2,767	2,856
Losses (gains) on investment securities available-for-sale	345
Losses (gains) on investment securities available-for-sale (including equity securities)		(4,340)	(1,796)
Originations of loans held for sale, net of principal collected	(78,450)	(101,104)	(119,134)
Proceeds from the sales of loans held for sale	82,127	106,811	116,397
Net gains on sale of loans held for sale	(1,844)	(2,981)	(3,287)
Net gain on sale of other real estate and repossessions	(561)	(251)	(228)
Change in interest receivable	(1,747)	(2,119)	(1,326)
Change in interest payable	2,997	1,222	570
Change in other assets	(8,076)	(1,434)	2,145
Change in other liabilities	7,375	(3,268)	648
Other	1,028	4,550	450
Net change in operating activities	144,374	117,261	98,060
Investing activities:
Proceeds from sales of investment securities available-for-sale	11,392
Proceeds from sales of investment securities available-for-sale (including equity securities)		228,715	23,784
Proceeds from maturities and paydowns of investment securities available-for-sale	145,167	177,466	217,613
Purchases of investment securities available-for-sale	(255,205)
Purchases of investment securities available-for-sale (including equity securities)		(469,385)	(313,074)
Proceeds from liquidation of partnership investment	1,868	128	2,903
Net change in other investments	(2,451)	(3,495)	(485)
Loans sold or participated to others	22,835	32,004	5,926
Net change in loans and leases	(355,504)	(382,386)	(209,668)
Net change in equipment owned under operating leases	(21,107)	(46,003)	(30,100)
Purchases of premises and equipment	(3,058)	(5,444)	(8,935)
Proceeds from sales of other real estate and repossessions	13,433	6,194	2,189
Net change in investing activities	(442,630)	(462,206)	(309,847)
Financing activities:
Net change in demand deposits and savings accounts	171,799	205,649	278,666
Net change in time deposits	197,793	213,321	(84,092)
Net change in short-term borrowings	(15,251)	(77,348)	58,714
Proceeds from issuance of long-term debt	0	19,999	20,837
Payments on long-term debt	(1,735)	(26,628)	(6,429)
Stock issued under stock purchase plans	145	153	120
Acquisition of treasury stock	(9,271)	(41)	(8,030)
Contributions from noncontrolling interests	1,508	0	0
Cash dividends paid on common stock	(25,686)	(20,431)	(19,416)
Net change in financing activities	319,302	314,674	240,370
Net change in cash and cash equivalents	21,046	(30,271)	28,583
Cash and cash equivalents, beginning of year	78,033	108,304	79,721
Cash and cash equivalents, end of year	99,079	78,033	108,304
Non-cash transactions:
Loans transferred to other real estate and repossessions	11,007	8,135	4,961
Common stock matching contribution to Employee Stock Ownership and Profit Sharing Plan	583	1,426	800
Cash paid for:
Interest	40,413	25,531	21,531
Income taxes	$ 8,272	$ 10,567	$ 19,866