Bank segment - Credit risk profile - assigned grades (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	$ 5,008,145	$ 4,843,634
Commercial Portfolio Segment
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	1,485,374	1,428,553
Commercial Portfolio Segment | Pass
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	1,339,514	1,295,902
Commercial Portfolio Segment | Special mention
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	39,275	44,469
Commercial Portfolio Segment | Substandard
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	97,759	88,182
Commercial Portfolio Segment | Doubtful
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	8,826	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	790,174	748,398
Commercial real estate | Pass
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	703,028	658,288
Commercial real estate | Special mention
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	11,012	32,871
Commercial real estate | Substandard
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	76,134	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	68,676	92,264
Commercial construction | Pass
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	66,387	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	626,524	587,891
Commercial loans | Pass
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	570,099	547,640
Commercial loans | Special mention
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	28,263	11,598
Commercial loans | Substandard
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	19,336	28,653
Commercial loans | Doubtful
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	8,826	0
Commercial loans | Loss
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	$ 0	$ 0