Bank segment - Credit risk profile - assigned grades (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	$ 4,858,270	$ 4,843,634
Commercial Portfolio Segment
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	1,412,458	1,428,553
Commercial Portfolio Segment | Pass
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	1,290,425	1,295,902
Commercial Portfolio Segment | Special mention
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	19,108	44,469
Commercial Portfolio Segment | Substandard
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	102,925	88,182
Commercial Portfolio Segment | Doubtful
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	0	0
Commercial Portfolio Segment | Loss
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	0	0
Commercial real estate
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	737,489	748,398
Commercial real estate | Pass
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	659,853	658,288
Commercial real estate | Special mention
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	7,960	32,871
Commercial real estate | Substandard
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	69,676	57,239
Commercial real estate | Doubtful
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	0	0
Commercial real estate | Loss
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	0	0
Commercial construction
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	98,734	92,264
Commercial construction | Pass
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	96,445	89,974
Commercial construction | Special mention
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	0	0
Commercial construction | Substandard
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	2,289	2,290
Commercial construction | Doubtful
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	0	0
Commercial construction | Loss
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	0	0
Commercial loans
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	576,235	587,891
Commercial loans | Pass
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	534,127	547,640
Commercial loans | Special mention
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	11,148	11,598
Commercial loans | Substandard
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	30,960	28,653
Commercial loans | Doubtful
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	0	0
Commercial loans | Loss
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	$ 0	$ 0