Income Taxes - Additional Information (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Loss Carryforwards [Line Items]
Net deferred tax assets	$ 66,800,000	$ 66,858,000
Deferred tax assets not related to net operating losses or credits	38,700,000
Alternative minimum tax credits	2,136,000	1,304,000
U.S. federal tax rate	35.00%	35.00%	35.00%
Income taxes related to securities transactions	181,000	162,000	2,939,000
Deferred Tax Assets Related to State Net Operating Losses	7,500,000
Minimum [Member]
Operating Loss Carryforwards [Line Items]
Annual income before taxes	2,100,000
Federal [Member]
Operating Loss Carryforwards [Line Items]
Net deferred tax assets	14,200,000
U.S. Federal [Member]
Operating Loss Carryforwards [Line Items]
Net deferred tax assets	52,600,000
Alternative minimum tax credits	$ 44,800,000