Stock-Based Compensation - Restricted Stock Unit Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Shares
Vested (in shares)	(48,890)	(981,633)
Restricted Stock
Shares
Balance at beginning of year (in shares)	1,359,162	1,463,796	1,204,883
Granted (in shares)		1,090,000	845,862
Forfeited (in shares)	(199,995)	(213,001)	(205,033)
Vested (in shares)	(48,890)	(981,633)	(381,916)
Balance at end of year (in shares)	1,110,277	1,359,162	1,463,796
Weighted Average Grant Date Fair Value
Balance at beginning of year (in dollars per share)	$ 1.28	$ 2.82	$ 4.21
Granted (in dollars per share)		0.97	1.88
Forfeited (in dollars per share)	1.59	2.99	4.25
Vested (in dollars per share)	1.59	2.85	4.36
Balance at end of year (in dollars per share)	$ 1.21	$ 1.28	$ 2.82