Tax Credit Investments - Narrative (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($) fund	Dec. 31, 2017 USD ($)	Dec. 31, 2019 USD ($) fund	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Schedule of Equity Method Investments [Line Items]
Number of federal renewable energy tax credit funds | fund	3		3
Federal renewable energy tax credit investments, net			$ 2,400
Federal renewable energy tax credit investments, net, amount per fund			800
Other tax credit investments, net			59,100
Other than temporary impairment losses on other tax credits investments	$ 2,400
Amortization Recorded in Non-Interest Expenses
Schedule of Equity Method Investments [Line Items]
Affordable housing tax credit investment impairment losses		$ 2,200	3,295	$ 2,544	$ 4,684
Other tax credit investment impairment losses		$ 2,100	$ 9,245	$ 17,806	$ 31,449