Federal Funds Purchased and Securities Sold Under Agreements to Repurchase (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Amount
At period-end	$ 313,773	$ 288,231
Rate
Repurchase agreement	238,300	219,900
Carrying amount of the securities pledged to collateralize repurchase agreements	238,300	219,900
Federal funds purchased and securities sold under repurchase agreements
Amount
At period-end	313,773	288,231	$ 221,541
Average for the year	320,901	291,428	253,948
Maximum month-end balance	$ 334,260	$ 320,373	$ 321,733
Rate
At period-end (as a percent)	0.24%	0.19%	0.14%
Average for the year (as a percent)	0.18%	0.14%	0.14%
Federal funds purchased and securities sold under repurchase agreements | Minimum
Information concerning federal funds purchased and securities sold under repurchase agreements
Maturity period from the transaction date	1 day
Federal funds purchased and securities sold under repurchase agreements | Maximum
Information concerning federal funds purchased and securities sold under repurchase agreements
Maturity period from the transaction date	3 days
Maturity period as per policies	9 months