Portfolio loans - Allowance for Loan Loss (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Dec. 31, 2016
Changes in allowance for loan losses
Beginning balance	$ 47,795	$ 47,487
Provision for loan loss	500	1,000
Charged-off	(1,232)	(3,871)
Recoveries	1,379	555
Ending Balance	48,442	45,171
Amount allocated to:
Loans individually evaluated for impairment			$ 2,902	$ 3,467
Loans collectively evaluated for impairment			45,540	44,328
Ending Balance	47,795	47,487	48,442	47,795
Loans:
Loans individually evaluated for impairment			34,377	35,175
Loans collectively evaluated for impairment			3,837,151	3,842,183
Ending Balance			3,872,952	3,878,900
Purchased Credit Impaired Loans
Loans:
Loans collectively evaluated for impairment			1,424	1,542
Commercial
Changes in allowance for loan losses
Beginning balance	13,303	13,115
Provision for loan loss	(649)	3,411
Charged-off	(103)	(3,552)
Recoveries	709	349
Ending Balance	13,260	13,323
Amount allocated to:
Loans individually evaluated for impairment			1,513	1,535
Loans collectively evaluated for impairment			11,747	11,768
Ending Balance	13,303	13,115	13,260	13,303
Loans:
Loans individually evaluated for impairment			11,380	11,834
Loans collectively evaluated for impairment			959,013	947,993
Ending Balance			970,451	959,888
Commercial \| Purchased Credit Impaired Loans
Loans:
Loans collectively evaluated for impairment			58	61
Commercial real estate
Changes in allowance for loan losses
Beginning balance	20,623	18,604
Provision for loan loss	(220)	(379)
Charged-off	(588)
Recoveries	33	15
Ending Balance	19,848	18,240
Amount allocated to:
Loans individually evaluated for impairment			1,247	1,778
Loans collectively evaluated for impairment			18,601	18,845
Ending Balance	20,623	18,604	19,848	20,623
Loans:
Loans individually evaluated for impairment			11,056	11,147
Loans collectively evaluated for impairment			1,647,052	1,642,010
Ending Balance			1,659,077	1,654,164
Commercial real estate \| Purchased Credit Impaired Loans
Loans:
Loans collectively evaluated for impairment			969	1,007
Real estate construction
Changes in allowance for loan losses
Beginning balance	1,870	1,763
Provision for loan loss	134	11
Recoveries	17	62
Ending Balance	2,021	1,836
Amount allocated to:
Loans individually evaluated for impairment				11
Loans collectively evaluated for impairment			2,021	1,859
Ending Balance	1,870	1,763	2,021	1,870
Loans:
Loans individually evaluated for impairment			470	494
Loans collectively evaluated for impairment			169,195	181,584
Ending Balance			169,665	182,078
Retail real estate
Changes in allowance for loan losses
Beginning balance	11,648	13,714
Provision for loan loss	1,220	(2,102)
Charged-off	(451)	(198)
Recoveries	561	73
Ending Balance	12,978	11,487
Amount allocated to:
Loans individually evaluated for impairment			140	140
Loans collectively evaluated for impairment			12,838	11,508
Ending Balance	11,648	13,714	12,978	11,648
Loans:
Loans individually evaluated for impairment			11,422	11,644
Loans collectively evaluated for impairment			1,049,146	1,056,942
Ending Balance			1,060,965	1,069,060
Retail real estate \| Purchased Credit Impaired Loans
Loans:
Loans collectively evaluated for impairment			397	474
Retail other
Changes in allowance for loan losses
Beginning balance	351	291
Provision for loan loss	15	59
Charged-off	(90)	(121)
Recoveries	59	56
Ending Balance	335	285
Amount allocated to:
Loans individually evaluated for impairment			2	3
Loans collectively evaluated for impairment			333	348
Ending Balance	$ 351	$ 291	335	351
Loans:
Loans individually evaluated for impairment			49	56
Loans collectively evaluated for impairment			12,745	13,654
Ending Balance			$ 12,794	$ 13,710

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Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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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 to estimated loss from loan and lease transactions.

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