Bank segment - Allowance for loan losses (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Allowance for loan losses:
Valuation allowance, balance at the beginning of the period	$ 45,618	$ 40,116
Charge-offs	(1,147)	(957)
Recoveries	710	769
Provision	614	995
Valuation allowance, balance at the end of the period	45,795	40,923
Ending balance: individually evaluated for impairment	5,548	5,685
Ending balance: collectively evaluated for impairment	40,247	35,238
Financing Receivables:
Total financing receivables	4,453,531us-gaap_NotesReceivableNet	4,196,369us-gaap_NotesReceivableNet	4,440,989us-gaap_NotesReceivableNet
Ending balance: individually evaluated for impairment	48,983	55,631
Ending balance: collectively evaluated for impairment	4,404,548	4,140,738
Residential 1-4 family
Allowance for loan losses:
Valuation allowance, balance at the beginning of the period	4,662	5,534
Charge-offs	(156)	(266)
Recoveries	12	341
Provision	403	(134)
Valuation allowance, balance at the end of the period	4,921	5,475
Ending balance: individually evaluated for impairment	1,429	906
Ending balance: collectively evaluated for impairment	3,492	4,569
Financing Receivables:
Total financing receivables	2,039,099	1,985,812	2,044,205
Ending balance: individually evaluated for impairment	23,089	20,141
Ending balance: collectively evaluated for impairment	2,016,010	1,965,671
Commercial real estate
Allowance for loan losses:
Valuation allowance, balance at the beginning of the period	8,954	5,059
Provision	2,274	656
Valuation allowance, balance at the end of the period	11,228	5,715
Ending balance: individually evaluated for impairment	1,785	1,544
Ending balance: collectively evaluated for impairment	9,443	4,171
Financing Receivables:
Total financing receivables	561,189	452,303	531,917
Ending balance: individually evaluated for impairment	4,998	4,558
Ending balance: collectively evaluated for impairment	556,191	447,745
Home equity line of credit
Allowance for loan losses:
Valuation allowance, balance at the beginning of the period	6,982	5,229
Charge-offs	(3)	0
Recoveries	31	11
Provision	(487)	729
Valuation allowance, balance at the end of the period	6,523	5,969
Ending balance: individually evaluated for impairment	144	0
Ending balance: collectively evaluated for impairment	6,379	5,969
Financing Receivables:
Total financing receivables	814,265	764,483	818,815
Ending balance: individually evaluated for impairment	1,183	1,164
Ending balance: collectively evaluated for impairment	813,082	763,319
Residential land
Allowance for loan losses:
Valuation allowance, balance at the beginning of the period	1,875	1,817
Charge-offs	0	(6)
Recoveries	49	86
Provision	362	(322)
Valuation allowance, balance at the end of the period	2,286	1,575
Ending balance: individually evaluated for impairment	1,085	1,102
Ending balance: collectively evaluated for impairment	1,201	473
Financing Receivables:
Total financing receivables	18,155	15,906	16,240
Ending balance: individually evaluated for impairment	7,819	10,351
Ending balance: collectively evaluated for impairment	10,336	5,555
Commercial construction
Allowance for loan losses:
Valuation allowance, balance at the beginning of the period	5,471	2,397
Provision	(2,634)	666
Valuation allowance, balance at the end of the period	2,837	3,063
Ending balance: collectively evaluated for impairment	2,837	3,063
Financing Receivables:
Total financing receivables	77,164	66,578	96,438
Ending balance: collectively evaluated for impairment	77,164	66,578
Residential construction
Allowance for loan losses:
Valuation allowance, balance at the beginning of the period	28	19
Provision	(7)	5
Valuation allowance, balance at the end of the period	21	24
Ending balance: collectively evaluated for impairment	21	24
Financing Receivables:
Total financing receivables	20,804	16,474	18,961
Ending balance: collectively evaluated for impairment	20,804	16,474
Commercial loans
Allowance for loan losses:
Valuation allowance, balance at the beginning of the period	14,017	15,803
Charge-offs	(46)	(124)
Recoveries	341	100
Provision	268	(187)
Valuation allowance, balance at the end of the period	14,580	15,592
Ending balance: individually evaluated for impairment	1,096	2,133
Ending balance: collectively evaluated for impairment	13,484	13,459
Financing Receivables:
Total financing receivables	803,545	786,611	791,757
Ending balance: individually evaluated for impairment	11,879	19,399
Ending balance: collectively evaluated for impairment	791,666	767,212
Consumer loans
Allowance for loan losses:
Valuation allowance, balance at the beginning of the period	3,629	2,367
Charge-offs	(942)	(561)
Recoveries	277	231
Provision	435	279
Valuation allowance, balance at the end of the period	3,399	2,316
Ending balance: individually evaluated for impairment	9
Ending balance: collectively evaluated for impairment	3,390	2,316
Financing Receivables:
Total financing receivables	119,310	108,202	122,656
Ending balance: individually evaluated for impairment	15	18
Ending balance: collectively evaluated for impairment	119,295	108,184
Unallocated
Allowance for loan losses:
Valuation allowance, balance at the beginning of the period	0	1,891
Provision	0	(697)
Valuation allowance, balance at the end of the period	0	1,194
Ending balance: collectively evaluated for impairment	$ 0	$ 1,194

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

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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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Net amount of the investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, credit card receivables, notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets. Excludes trade accounts receivable with contractual maturity of one year or less and arose from the sale of goods or services.

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- Definition

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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