Bank segment - Credit risk profile - assigned grades (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross	$ 5,389,443	$ 5,067,821
Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		824,830
Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		70,605
Commercial
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		670,674
Commercial Real Estate, Commercial Construction And Commercial Portfolio Segment
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		1,566,109
Pass | Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		756,747
Pass | Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		68,316
Pass | Commercial
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		621,657
Pass | Commercial Real Estate, Commercial Construction And Commercial Portfolio Segment
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		1,446,720
Special Mention | Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		4,451
Special Mention | Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		0
Special Mention | Commercial
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		29,921
Special Mention | Commercial Real Estate, Commercial Construction And Commercial Portfolio Segment
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		34,372
Substandard | Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		63,632
Substandard | Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		2,289
Substandard | Commercial
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		19,096
Substandard | Commercial Real Estate, Commercial Construction And Commercial Portfolio Segment
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		85,017
Doubtful | Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		0
Doubtful | Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		0
Doubtful | Commercial
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		0
Doubtful | Commercial Real Estate, Commercial Construction And Commercial Portfolio Segment
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		0
Loss | Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		0
Loss | Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		0
Loss | Commercial
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		0
Loss | Commercial Real Estate, Commercial Construction And Commercial Portfolio Segment
Credit risk profile by internally assigned grade for loans
Loans and leases receivable before fees, gross		$ 0