Reserve for Loan and Lease Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015
Changes in reserve for loan and lease losses
Balance at the beginning of the period	$ 88,112	$ 85,068	$ 83,505
Charge-offs	7,941	4,710	6,031
Recoveries	2,539	5,594	3,861
Net charge-offs (recoveries)	5,402	(884)	2,170
Provision (recovery of provision)	5,833	2,160	3,733
Balance at the end of the period	88,543	88,112	85,068
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment				$ 1,878	$ 797
Ending balance, collectively evaluated for impairment				86,665	87,315
Total reserve for loan and lease losses	88,112	85,068	83,505	88,543	88,112
Recorded investment in loans
Ending balance, individually evaluated for impairment				17,028	17,683
Ending balance, collectively evaluated for impairment				4,171,043	3,977,009
Total loans and leases				4,188,071	3,994,692
Commercial and agricultural
Changes in reserve for loan and lease losses
Balance at the beginning of the period	15,456	11,760	11,515
Charge-offs	547	3,489	5,007
Recoveries	509	851	929
Net charge-offs (recoveries)	38	2,638	4,078
Provision (recovery of provision)	(750)	6,334	4,323
Balance at the end of the period	14,668	15,456	11,760
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment				297	649
Ending balance, collectively evaluated for impairment				14,371	14,807
Total reserve for loan and lease losses	15,456	11,760	11,515	14,668	15,456
Recorded investment in loans
Ending balance, individually evaluated for impairment				3,590	3,900
Ending balance, collectively evaluated for impairment				808,674	740,849
Total loans and leases				812,264	744,749
Auto and light truck
Changes in reserve for loan and lease losses
Balance at the beginning of the period	9,269	10,326	9,657
Charge-offs	4	24	42
Recoveries	253	380	1,283
Net charge-offs (recoveries)	(249)	(356)	(1,241)
Provision (recovery of provision)	(1,454)	(1,413)	(572)
Balance at the end of the period	8,064	9,269	10,326
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment				0	0
Ending balance, collectively evaluated for impairment				8,064	9,269
Total reserve for loan and lease losses	9,269	10,326	9,657	8,064	9,269
Recorded investment in loans
Ending balance, individually evaluated for impairment				115	0
Ending balance, collectively evaluated for impairment				411,649	425,236
Total loans and leases				411,764	425,236
Medium and heavy duty truck
Changes in reserve for loan and lease losses
Balance at the beginning of the period	4,699	4,500	4,212
Charge-offs	0	0	0
Recoveries	10	28	142
Net charge-offs (recoveries)	(10)	(28)	(142)
Provision (recovery of provision)	31	171	146
Balance at the end of the period	4,740	4,699	4,500
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment				0	0
Ending balance, collectively evaluated for impairment				4,740	4,699
Total reserve for loan and lease losses	4,699	4,500	4,212	4,740	4,699
Recorded investment in loans
Ending balance, individually evaluated for impairment				0	0
Ending balance, collectively evaluated for impairment				294,790	278,254
Total loans and leases				294,790	278,254
Aircraft
Changes in reserve for loan and lease losses
Balance at the beginning of the period	32,373	32,234	34,037
Charge-offs	6,123	244	0
Recoveries	528	802	240
Net charge-offs (recoveries)	5,595	(558)	(240)
Provision (recovery of provision)	7,574	(419)	(2,043)
Balance at the end of the period	34,352	32,373	32,234
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment				1,076	0
Ending balance, collectively evaluated for impairment				33,276	32,373
Total reserve for loan and lease losses	32,373	32,234	34,037	34,352	32,373
Recorded investment in loans
Ending balance, individually evaluated for impairment				6,110	4,384
Ending balance, collectively evaluated for impairment				796,304	773,628
Total loans and leases				802,414	778,012
Construction equipment
Changes in reserve for loan and lease losses
Balance at the beginning of the period	7,592	7,008	5,972
Charge-offs	128	0	4
Recoveries	461	434	525
Net charge-offs (recoveries)	(333)	(434)	(521)
Provision (recovery of provision)	282	150	515
Balance at the end of the period	8,207	7,592	7,008
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment				35	0
Ending balance, collectively evaluated for impairment				8,172	7,592
Total reserve for loan and lease losses	7,592	7,008	5,972	8,207	7,592
Recorded investment in loans
Ending balance, individually evaluated for impairment				1,167	539
Ending balance, collectively evaluated for impairment				494,758	455,026
Total loans and leases				495,925	455,565
Commercial real estate
Changes in reserve for loan and lease losses
Balance at the beginning of the period	13,762	13,270	12,406
Charge-offs	32	0	99
Recoveries	469	2,807	347
Net charge-offs (recoveries)	(437)	(2,807)	(248)
Provision (recovery of provision)	(522)	(2,315)	616
Balance at the end of the period	13,677	13,762	13,270
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment				322	0
Ending balance, collectively evaluated for impairment				13,355	13,762
Total reserve for loan and lease losses	13,762	13,270	12,406	13,677	13,762
Recorded investment in loans
Ending balance, individually evaluated for impairment				5,372	8,494
Ending balance, collectively evaluated for impairment				713,798	691,774
Total loans and leases				719,170	700,268
Residential real estate and home equity
Changes in reserve for loan and lease losses
Balance at the beginning of the period	3,662	4,504	4,539
Charge-offs	219	295	46
Recoveries	31	34	111
Net charge-offs (recoveries)	188	261	(65)
Provision (recovery of provision)	76	(581)	(100)
Balance at the end of the period	3,550	3,662	4,504
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment				148	148
Ending balance, collectively evaluated for impairment				3,402	3,514
Total reserve for loan and lease losses	3,662	4,504	4,539	3,550	3,662
Recorded investment in loans
Ending balance, individually evaluated for impairment				674	366
Ending balance, collectively evaluated for impairment				521,257	490,102
Total loans and leases				521,931	490,468
Consumer
Changes in reserve for loan and lease losses
Balance at the beginning of the period	1,299	1,466	1,167
Charge-offs	888	658	833
Recoveries	278	258	284
Net charge-offs (recoveries)	610	400	549
Provision (recovery of provision)	596	233	848
Balance at the end of the period	1,285	1,299	1,466
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment				0	0
Ending balance, collectively evaluated for impairment				1,285	1,299
Total reserve for loan and lease losses	$ 1,299	$ 1,466	$ 1,167	1,285	1,299
Recorded investment in loans
Ending balance, individually evaluated for impairment				0	0
Ending balance, collectively evaluated for impairment				129,813	122,140
Total loans and leases				$ 129,813	$ 122,140