Portfolio loans - Distribution (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Portfolio Loans
Portfolio loans	$ 6,515,081	$ 5,568,428
Allowance for loan losses	(50,915)	(50,648)	$ (52,649)	$ (53,582)
Portfolio loans, net	6,464,166	5,517,780
Net deferred loan origination costs	5,400	5,600
Amount of loan reduction due to net accretable purchase accounting adjustments	28,200	13,900
Commercial
Portfolio Loans
Portfolio loans	1,657,022	1,405,106
Allowance for loan losses	(17,998)	(17,829)	(17,577)	(14,779)
Commercial real estate
Portfolio Loans
Portfolio loans	2,699,491	2,366,823
Allowance for loan losses	(20,097)	(21,137)	(22,090)	(21,813)
Real estate construction
Portfolio Loans
Portfolio loans	387,623	288,197
Allowance for loan losses	(2,807)	(2,723)	(2,799)	(2,861)
Retail real estate
Portfolio Loans
Portfolio loans	1,718,415	1,480,133
Allowance for loan losses	(9,503)	(8,471)	(9,836)	(13,783)
Retail other
Portfolio Loans
Portfolio loans	52,530	28,169
Allowance for loan losses	$ (510)	$ (488)	$ (347)	$ (346)

Amount of loans increased (decrease) due to net accretable purchase accounting adjustments.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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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 after allowance and 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 and loans held for sale.

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