Investment Securities - Income Earned on Securities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Non-taxable:
Total	$ 13,473	$ 15,666	$ 32,416	$ 31,947
Held-to-maturity
Taxable:
Taxable	288	289	459	727
Non-taxable:
Non-taxable	68	89	140	1,251
Available-for-sale
Taxable:
Taxable	7,086	10,777	19,667	22,297
Non-taxable:
Non-taxable	$ 6,031	$ 4,511	$ 12,150	$ 7,672