Stock-Based Compensation - Narrative (Details) - USD ($) $ in Millions			12 Months Ended
	May 25, 2016	Apr. 12, 2010	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 21, 2018	Dec. 31, 2015	May 29, 2010
Stock Based Compensation Details [Line Items]
Shares of common stock outstanding			53,774,221	53,400,281
Intrinsic value of options outstanding			$ 0.5	$ 4.7	$ 11.5
Intrinsic value of options exercisable			0.5	4.7	11.3
Intrinsic value of options exercised			0.1	0.4	0.3
Unrecognized compensation costs			1.2
General and Administrative Expense
Stock Based Compensation Details [Line Items]
Stock option based expenses			$ 1.5	$ 2.3	$ 2.3
Director Stock Option Plan - 1999
Stock Based Compensation Details [Line Items]
Shares approved and authorized (in shares)				1,975,000
Number of options granted (in shares)				2,634,798
Number of options forfeited (in shares)				807,782
Vesting period			1 year
Maximum term			10 years
Number of options outstanding (in shares)			500,000	500,000
Shares available for grant				147,984
Nineteen Ninety Nine Stock Incentive Plan
Stock Based Compensation Details [Line Items]
Shares approved and authorized (in shares)			3,200,000
Number of options granted (in shares)			2,892,500
Vesting period			4 years
Maximum term			10 years
Percent of FMV options granted			100.00%
Service period			1 year
Plan 2009
Stock Based Compensation Details [Line Items]
Shares approved and authorized (in shares)	2,500,000							5,000,000
Number of options outstanding (in shares)			2,458,106
Additional shares authorized (in shares)		2,000,000
Maximum number of shares to any individual (in shares)			1,000,000
Shares of common stock outstanding			1,853,925	1,422,020
Options transferred (in shares)			346,504	249,052
Plan 2016
Stock Based Compensation Details [Line Items]
Shares approved and authorized (in shares)	2,000,000					4,000,000
Shares available for grant			3,113,374	1,526,857
Maximum number of shares to any individual (in shares)	1,000,000
Shares of common stock outstanding			74,667	20,000
Plan 2016, Plan 2009 And Director Plan
Stock Based Compensation Details [Line Items]
Number of options outstanding (in shares)			4,352,391	4,299,810
Restricted Stock Units (RSUs)
Stock Based Compensation Details [Line Items]
RSUs outstanding (in shares)			175,591	188,629	179,900		182,750
Restricted Stock Units (RSUs) | Plan 2009
Stock Based Compensation Details [Line Items]
RSUs outstanding (in shares)			14,377	99,626
Restricted Stock Units (RSUs) | Plan 2016
Stock Based Compensation Details [Line Items]
RSUs outstanding (in shares)			161,214
Shares of common stock outstanding				89,003
Restricted Stock
Stock Based Compensation Details [Line Items]
Stock option based expenses			$ 0.5	$ 1.0	$ 0.8
Unrecognized compensation costs			$ 0.5
Common Stock | Plan 2009
Stock Based Compensation Details [Line Items]
Number of options outstanding (in shares)				3,038,634
Common Stock | Plan 2016
Stock Based Compensation Details [Line Items]
Number of options outstanding (in shares)			1,394,285	761,176
Minimum | Restricted Stock
Stock Based Compensation Details [Line Items]
Vesting period			1 year
Maximum | Restricted Stock
Stock Based Compensation Details [Line Items]
Vesting period			3 years