Investment Securities - Income Earned on Securities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Non-taxable:
Total	$ 14,910	$ 14,467	$ 47,326	$ 46,414
Held-to-maturity
Taxable:
Taxable	256	248	715	975
Non-taxable:
Non-taxable	65	83	205	1,334
Available-for-sale
Taxable:
Taxable	6,937	9,266	26,604	31,563
Non-taxable:
Non-taxable	$ 7,652	$ 4,870	$ 19,802	$ 12,542