Investment Securities - Income Earned on Securities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Non-taxable:
Total	$ 16,594	$ 14,296	$ 33,906	$ 26,918
Held-to-maturity
Taxable:
Taxable	289	546	727	1,113
Non-taxable:
Non-taxable	89	1,897	1,251	3,833
Available-for-sale
Taxable:
Taxable	11,705	10,218	24,256	19,250
Non-taxable:
Non-taxable	$ 4,511	$ 1,635	$ 7,672	$ 2,722