Borrowings - Schedule of contractual maturity of borrowings (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Total FHLB advances	$ 1,407,022	$ 1,189,180
Line of Credit and FHLB Advances
Debt Instrument [Line Items]
One year or less	1,004,139
After one year to two years	178,723
After two years to three years	169,800
After three years to four years	20,529
After four years	10,000
Total FHLB advances	$ 1,383,191