Short-Term Borrowings and Long-Term FHLB Advances - Information Concerning Short-term Borrowings (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Long-term Federal Home Loan Bank Advances [Abstract]
Balance at period-end	$ 227,059	$ 130,295	$ 227,059	$ 130,295	$ 237,865
Maximum amount outstanding at any month end	279,525	130,295	279,525	130,295
Average balance outstanding during the period	$ 218,566	$ 98,869	$ 198,079	$ 73,378
Short-term debt, weighted average interest rate at period end (as a percent)	1.89%	1.11%	1.89%	1.11%
Paid during the period (as a percent)	1.92%	0.96%	1.72%	0.72%