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
Amount
At period-end	$ 288,231	$ 221,541
Rate
Repurchase agreement	219,900	160,900
Carrying amount of the securities pledged to collateralize repurchase agreements	219,900	160,900
Federal funds purchased and securities sold under repurchase agreements
Amount
At period-end	288,231	221,541	$ 211,401
Average for the year	291,428	253,948	274,080
Maximum month-end balance	$ 320,373	$ 321,733	$ 328,701
Rate
At period-end (as a percent)	0.19%	0.14%	0.14%
Average for the year (as a percent)	0.14%	0.14%	0.16%
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