Debt Securities - Gain or Loss on Sale (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Available-for-sale
Proceeds from sales and calls of debt securities		$ 240,521	$ 928,710	$ 265,587
Gross realized gains	[1]	1,400	18,936	443
Gross realized losses	[1]	(262)	(4,513)	(455)
Held-to-maturity
Proceeds from calls of debt securities		32,735	58,750	79,000
Gross realized gains	[1]	1	2	101
Gross realized losses	[1]	$ 0	$ (10)	$ (1,202)

[1] The gain or loss on the sale or call of each debt security is determined by the specific identification method.