Borrowings - Federal Funds Purchased and Securities Sold Under Agreements to Repurchase (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
Maximum amount outstanding at any month end	$ 341,213	$ 216,094	$ 236,099
Weighted average interest rate at end of year	1.14%	0.71%	0.31%
Average amount outstanding	$ 200,839	$ 171,686	$ 187,560
Weighted average interest rate during the year	0.90%	0.46%	0.26%