Securities - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, pledged	$ 1,200,000,000	$ 1,200,000,000	$ 1,100,000,000
Debt securities, held-to-maturity, pledged	0	0	0
Purchases of securities	47,100,000	$ 735,701,000	733,440,000	$ 933,317,000
Securities sold	$ 25,000,000
Net realized (losses) gains on sales of securities			(1,876,000)	1,420,000
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Net realized (losses) gains on sales of securities			(3,200,000)	1,100,000
Equity securities
Debt Securities, Available-for-sale [Line Items]
Net realized (losses) gains on sales of securities			$ 1,300,000	$ 304,000