Borrowings - Schedule of borrowed funds (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Borrowings	$ 1,189,180	$ 929,057
Weighted average interest rate	2.43%	2.25%
Lines of credit
Debt Instrument [Line Items]
Borrowings	$ 159,600	$ 46,000
Weighted average interest rate	2.60%	1.53%
Federal Home Loan Bank advances
Debt Instrument [Line Items]
Borrowings	$ 1,029,580	$ 822,400
Weighted average interest rate	2.40%	1.92%
Junior subordinated debt
Debt Instrument [Line Items]
Borrowings	$ 0	$ 50,657
Weighted average interest rate	0.00%	8.00%
Securities sold under agreements to repurchase
Debt Instrument [Line Items]
Borrowings	$ 0	$ 10,000
Weighted average interest rate	0.00%	3.23%