Reserve for Loan and Lease Losses (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015 item	Mar. 31, 2014	Dec. 31, 2014
Reserve for loan and lease losses
Number of classes existing in loan and lease portfolio	8
Changes in reserve for loan and lease losses
Balance at the beginning of the period	$ 85,068	$ 83,505
Charge-offs	1,201	303
Recoveries	874	1,004
Net charge-offs (recoveries)	327	(701)
Provision (recovery of provision)	357	804
Balance at the end of the period	85,098	85,010
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment	735	226
Ending balance, collectively evaluated for impairment	84,363	84,784
Total reserve for loan and lease losses	85,098	85,010
Recorded investment in loans
Ending balance, individually evaluated for impairment	26,724	29,854
Ending balance, collectively evaluated for impairment	3,674,408	3,547,714
Total loans and leases	3,701,132	3,577,568	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
Charge-offs	943	15
Recoveries	478	379
Net charge-offs (recoveries)	465	(364)
Provision (recovery of provision)	325	(60)
Balance at the end of the period	11,620	11,819
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment	13	0
Ending balance, collectively evaluated for impairment	11,607	11,819
Total reserve for loan and lease losses	11,620	11,819
Recorded investment in loans
Ending balance, individually evaluated for impairment	6,694	11,146
Ending balance, collectively evaluated for impairment	705,599	687,100
Total loans and leases	712,293	698,246	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
Charge-offs	22	11
Recoveries	60	234
Net charge-offs (recoveries)	(38)	(223)
Provision (recovery of provision)	429	(224)
Balance at the end of the period	10,793	9,656
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment	0	0
Ending balance, collectively evaluated for impairment	10,793	9,656
Total reserve for loan and lease losses	10,793	9,656
Recorded investment in loans
Ending balance, individually evaluated for impairment	0	266
Ending balance, collectively evaluated for impairment	402,389	388,399
Total loans and leases	402,389	388,665	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
Charge-offs	0	0
Recoveries	3	37
Net charge-offs (recoveries)	(3)	(37)
Provision (recovery of provision)	(139)	162
Balance at the end of the period	4,364	4,411
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment	0	0
Ending balance, collectively evaluated for impairment	4,364	4,411
Total reserve for loan and lease losses	4,364	4,411
Recorded investment in loans
Ending balance, individually evaluated for impairment	0	0
Ending balance, collectively evaluated for impairment	240,187	237,906
Total loans and leases	240,187	237,906	247,153
Aircraft financing
Changes in reserve for loan and lease losses
Balance at the beginning of the period	32,234	34,037
Charge-offs	49	0
Recoveries	44	57
Net charge-offs (recoveries)	5	(57)
Provision (recovery of provision)	(928)	415
Balance at the end of the period	31,301	34,509
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment	501	57
Ending balance, collectively evaluated for impairment	30,800	34,452
Total reserve for loan and lease losses	31,301	34,509
Recorded investment in loans
Ending balance, individually evaluated for impairment	7,379	4,147
Ending balance, collectively evaluated for impairment	689,564	726,656
Total loans and leases	696,943	730,803	727,665
Construction equipment financing
Changes in reserve for loan and lease losses
Balance at the beginning of the period	7,008	5,972
Charge-offs	0	2
Recoveries	122	166
Net charge-offs (recoveries)	(122)	(164)
Provision (recovery of provision)	610	178
Balance at the end of the period	7,740	6,314
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment	0	9
Ending balance, collectively evaluated for impairment	7,740	6,305
Total reserve for loan and lease losses	7,740	6,314
Recorded investment in loans
Ending balance, individually evaluated for impairment	734	1,129
Ending balance, collectively evaluated for impairment	438,796	351,667
Total loans and leases	439,530	352,796	399,940
Commercial real estate
Changes in reserve for loan and lease losses
Balance at the beginning of the period	13,270	12,406
Charge-offs	0	1
Recoveries	97	39
Net charge-offs (recoveries)	(97)	(38)
Provision (recovery of provision)	(181)	165
Balance at the end of the period	13,186	12,609
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment	67	0
Ending balance, collectively evaluated for impairment	13,119	12,609
Total reserve for loan and lease losses	13,186	12,609
Recorded investment in loans
Ending balance, individually evaluated for impairment	11,546	12,789
Ending balance, collectively evaluated for impairment	604,009	575,840
Total loans and leases	615,555	588,629	616,587
Residential real estate
Changes in reserve for loan and lease losses
Balance at the beginning of the period	4,102	4,093
Charge-offs	40	16
Recoveries	2	5
Net charge-offs (recoveries)	38	11
Provision (recovery of provision)	51	(20)
Balance at the end of the period	4,115	4,062
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment	154	160
Ending balance, collectively evaluated for impairment	3,961	3,902
Total reserve for loan and lease losses	4,115	4,062
Recorded investment in loans
Ending balance, individually evaluated for impairment	371	377
Ending balance, collectively evaluated for impairment	443,004	455,301
Total loans and leases	443,375	455,678	445,759
Consumer
Changes in reserve for loan and lease losses
Balance at the beginning of the period	1,868	1,613
Charge-offs	147	258
Recoveries	68	87
Net charge-offs (recoveries)	79	171
Provision (recovery of provision)	190	188
Balance at the end of the period	1,979	1,630
Reserve for loan and lease losses
Ending balance, individually evaluated for impairment	0	0
Ending balance, collectively evaluated for impairment	1,979	1,630
Total reserve for loan and lease losses	1,979	1,630
Recorded investment in loans
Ending balance, individually evaluated for impairment	0	0
Ending balance, collectively evaluated for impairment	150,860	124,845
Total loans and leases	$ 150,860	$ 124,845	$ 142,810

Amount of direct write-downs of financing receivables charged against the allowance net of recoveries.

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Represents the number of classes existing in loan and lease portfolio.

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A valuation allowance for financing receivables that are expected to be uncollectible.

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The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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Amount of recovery of financing receivables doubtful of collection that were previously charged off.

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Amount of direct write-downs of financing receivables charged against the allowance.

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The balance of financing receivables that were collectively evaluated for impairment.

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The balance of financing receivables that were individually evaluated for impairment.

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.

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