Selected Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenues	$ 44,184	$ 45,355	$ 44,635	$ 45,388	$ 47,339	$ 46,181	$ 47,969	$ 48,138	$ 179,561	$ 189,628	$ 200,273
Operating income	4,703	6,029	5,620	5,800	6,550	6,657	5,621	6,273	22,153	25,100	28,151
Net income	$ 3,026	$ 4,058	$ 3,451	$ 3,444	$ 68,732	$ 4,220	$ 3,376	$ 3,917	$ 13,979	$ 80,246	$ 20,745
Basic and diluted net income per common share (usd per share)	$ 0.15	$ 0.20	$ 0.17	$ 0.17	$ 3.28	$ 0.20	$ 0.16	$ 0.18	$ 0.68	$ 3.74	$ 0.96
Release from valuation allowance					$ 64,200
Decrease in deferred tax benefit									$ 6,926	$ (55,018)	$ 4,740
Net Operating Loss Carryforward Overstatement
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net income					68,732					80,246
Adjustment | Net Operating Loss Carryforward Overstatement
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net income					(3,989)					(3,989)
Decrease in deferred tax benefit					$ 4,000					$ 4,000