Borrowings - Federal Funds Purchased and Securities Sold Under Agreements to Repurchase (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Short-term Debt [Line Items]
Maximum amount outstanding at any month end	$ 230,120	$ 298,399	$ 165,770
Weighted average interest rate at end of year	0.28%	0.19%	0.17%
Average amount outstanding	$ 182,914	$ 171,965	$ 155,222
Weighted average interest rate during the year	0.21%	0.17%	0.18%