Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Loss Carryforwards [Line Items]
Net deferred tax assets	$ 60,274,000	$ 66,800,000
U.S. federal tax rate	35.00%	35.00%	35.00%
Income taxes related to securities transactions	$ 62,000	$ 181,000	$ 162,000
Deferred Tax Assets Related to State Net Operating Losses	6,800,000
Deferred Tax Assets, Operating Loss Carryforwards, Domestic	33,507,000	39,974,000
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	3,355,000	2,136,000
Deferred Tax Assets, Unrealized Losses on Available-for-Sale Securities, Gross	3,906,000	$ 3,035,000
Grand Bankshares [Member]
Operating Loss Carryforwards [Line Items]
Net deferred tax assets	5,300,000
Operating Loss Carryforwards Expired	22,700,000
Deferred Tax Assets, Operating Loss Carryforwards, Domestic	9,100,000
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	91,000
Operating Loss Carryforwards	31,800,000
Minimum [Member]
Operating Loss Carryforwards [Line Items]
Annual income before taxes	3,400,000
Federal [Member]
Operating Loss Carryforwards [Line Items]
Net deferred tax assets	$ 12,700,000
Federal [Member] | Maximum [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carry forwards Expiration Period	2032
Federal [Member] | Minimum [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carry forwards Expiration Period	2029
U.S. Federal [Member]
Operating Loss Carryforwards [Line Items]
Net deferred tax assets	$ 47,500,000
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	$ 44,800,000
State and Local Jurisdiction [Member] | Maximum [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carry forwards Expiration Period	2034
State and Local Jurisdiction [Member] | Minimum [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carry forwards Expiration Period	2028