Reserve for Loan and Lease Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014
Changes in reserve for loan and lease losses
Balance at the beginning of the period	$ 85,068	$ 83,505	$ 83,311
Charge-offs	4,710	6,031	3,828
Recoveries	5,594	3,861	3,250
Net charge-offs (recoveries)	(884)	2,170	578
Provision (recovery of provision)	2,160	3,733	772
Balance at the end of the period	88,112	85,068	83,505
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment				$ 797	$ 241
Ending balance, collectively evaluated for impairment				87,315	84,827
Total reserve for loan and lease losses	85,068	83,505	83,311	88,112	85,068
Recorded investment in loans
Ending balance, individually evaluated for impairment				17,683	40,906
Ending balance, collectively evaluated for impairment				3,977,009	3,647,668
Total loans and leases				3,994,692	3,688,574
Commercial and agricultural
Changes in reserve for loan and lease losses
Balance at the beginning of the period	11,760	11,515	12,326
Charge-offs	3,489	5,007	538
Recoveries	851	929	468
Net charge-offs (recoveries)	2,638	4,078	70
Provision (recovery of provision)	6,334	4,323	(741)
Balance at the end of the period	15,456	11,760	11,515
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment				649	5
Ending balance, collectively evaluated for impairment				14,807	11,755
Total reserve for loan and lease losses	11,760	11,515	12,326	15,456	11,760
Recorded investment in loans
Ending balance, individually evaluated for impairment				3,900	14,542
Ending balance, collectively evaluated for impairment				740,849	696,216
Total loans and leases				744,749	710,758
Auto and light truck
Changes in reserve for loan and lease losses
Balance at the beginning of the period	10,326	9,657	8,864
Charge-offs	24	42	226
Recoveries	380	1,283	139
Net charge-offs (recoveries)	(356)	(1,241)	87
Provision (recovery of provision)	(1,413)	(572)	880
Balance at the end of the period	9,269	10,326	9,657
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment				0	0
Ending balance, collectively evaluated for impairment				9,269	10,326
Total reserve for loan and lease losses	10,326	9,657	8,864	9,269	10,326
Recorded investment in loans
Ending balance, individually evaluated for impairment				0	0
Ending balance, collectively evaluated for impairment				425,236	397,902
Total loans and leases				425,236	397,902
Medium and heavy duty truck
Changes in reserve for loan and lease losses
Balance at the beginning of the period	4,500	4,212	3,721
Charge-offs	0	0	57
Recoveries	28	142	462
Net charge-offs (recoveries)	(28)	(142)	(405)
Provision (recovery of provision)	171	146	86
Balance at the end of the period	4,699	4,500	4,212
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment				0	0
Ending balance, collectively evaluated for impairment				4,699	4,500
Total reserve for loan and lease losses	4,500	4,212	3,721	4,699	4,500
Recorded investment in loans
Ending balance, individually evaluated for impairment				0	0
Ending balance, collectively evaluated for impairment				278,254	247,153
Total loans and leases				278,254	247,153
Aircraft financing
Changes in reserve for loan and lease losses
Balance at the beginning of the period	32,234	34,037	34,205
Charge-offs	244	0	1,308
Recoveries	802	240	884
Net charge-offs (recoveries)	(558)	(240)	424
Provision (recovery of provision)	(419)	(2,043)	256
Balance at the end of the period	32,373	32,234	34,037
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment				0	0
Ending balance, collectively evaluated for impairment				32,373	32,234
Total reserve for loan and lease losses	32,234	34,037	34,205	32,373	32,234
Recorded investment in loans
Ending balance, individually evaluated for impairment				4,384	12,740
Ending balance, collectively evaluated for impairment				773,628	714,925
Total loans and leases				778,012	727,665
Construction equipment financing
Changes in reserve for loan and lease losses
Balance at the beginning of the period	7,008	5,972	5,390
Charge-offs	0	4	88
Recoveries	434	525	323
Net charge-offs (recoveries)	(434)	(521)	(235)
Provision (recovery of provision)	150	515	347
Balance at the end of the period	7,592	7,008	5,972
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment				0	0
Ending balance, collectively evaluated for impairment				7,592	7,008
Total reserve for loan and lease losses	7,008	5,972	5,390	7,592	7,008
Recorded investment in loans
Ending balance, individually evaluated for impairment				539	746
Ending balance, collectively evaluated for impairment				455,026	399,194
Total loans and leases				455,565	399,940
Commercial real estate
Changes in reserve for loan and lease losses
Balance at the beginning of the period	13,270	12,406	13,778
Charge-offs	0	99	170
Recoveries	2,807	347	627
Net charge-offs (recoveries)	(2,807)	(248)	(457)
Provision (recovery of provision)	(2,315)	616	(1,829)
Balance at the end of the period	13,762	13,270	12,406
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment				0	80
Ending balance, collectively evaluated for impairment				13,762	13,190
Total reserve for loan and lease losses	13,270	12,406	13,778	13,762	13,270
Recorded investment in loans
Ending balance, individually evaluated for impairment				8,494	12,505
Ending balance, collectively evaluated for impairment				691,774	604,082
Total loans and leases				700,268	616,587
Residential real estate
Changes in reserve for loan and lease losses
Balance at the beginning of the period	4,102	4,093	3,652
Charge-offs	141	46	316
Recoveries	11	97	14
Net charge-offs (recoveries)	130	(51)	302
Provision (recovery of provision)	(590)	(42)	743
Balance at the end of the period	3,382	4,102	4,093
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment				148	156
Ending balance, collectively evaluated for impairment				3,234	3,946
Total reserve for loan and lease losses	4,102	4,093	3,652	3,382	4,102
Recorded investment in loans
Ending balance, individually evaluated for impairment				366	373
Ending balance, collectively evaluated for impairment				463,763	445,386
Total loans and leases				464,129	445,759
Consumer
Changes in reserve for loan and lease losses
Balance at the beginning of the period	1,868	1,613	1,375
Charge-offs	812	833	1,125
Recoveries	281	298	333
Net charge-offs (recoveries)	531	535	792
Provision (recovery of provision)	242	790	1,030
Balance at the end of the period	1,579	1,868	1,613
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment				0	0
Ending balance, collectively evaluated for impairment				1,579	1,868
Total reserve for loan and lease losses	$ 1,868	$ 1,613	$ 1,375	1,579	1,868
Recorded investment in loans
Ending balance, individually evaluated for impairment				0	0
Ending balance, collectively evaluated for impairment				148,479	142,810
Total loans and leases				$ 148,479	$ 142,810