Stock-Based Compensation - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of Options
Outstanding at beginning of year (in shares)	1,039,750	1,191,125	1,546,500
Granted (in shares)	176,000	81,000	126,000
Exercised (in shares)	0	0	0
Expired or forfeited (in shares)	(99,000)	(232,375)	(481,375)
Outstanding at end of year (in shares)	1,116,750	1,039,750	1,191,125
Exercisable at end of year (in shares)	1,116,750	1,039,750	1,191,125
Weighted- Average Exercise Price
Outstanding at beginning of year (in dollars per share)	$ 8.39	$ 10.48	$ 11.62
Granted (in dollars per share)	0.96	1.58	2.44
Exercised (in dollars per share)	0.00	0.00	0.00
Expired or forfeited (in dollars per share)	18.32	16.72	12.04
Outstanding at end of year (in dollars per share)	6.34	8.39	10.48
Exercisable at end of year (in dollars per share)	6.34	8.39	10.48
Weighted-average fair value of options granted during the year (in dollars per share)	$ 0.68	$ 1.11	$ 1.54