Stockholders' Equity - Additional Information (Details)		1 Months Ended				12 Months Ended
	Nov. 29, 2010	Aug. 31, 2017 USD ($)	Jun. 30, 2016 USD ($) shares	Dec. 31, 2015 USD ($)	Sep. 30, 2003 USD ($) shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 shares	Jun. 13, 2011 shares	Jun. 12, 2011 shares	Dec. 13, 2010 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares authorized (shares)						5,000,000	5,000,000
Number of common shares authorized (shares)						175,000,000	175,000,000	175,000,000	100,000,000
Threshold to exercise rights after designated events	10 days
Percentage of ownership of common stock required to exercise preferred share rights	15.00%
Percentage of ownership of common stock required to be held by designated holder to exercise preferred share purchase rights	20.00%
Waiting period after rights activated	5 days
Right to purchase shares	2
Transfer of assets or earnings power	50.00%
Preferred stock issued (shares)						0	0
Convertible preferred stock outstanding (shares)						0	0
Shares of common stock issuable upon conversion or exercise of rights granted (shares)						15,900,000
Maximum proceeds to be raised | $		$ 150,000,000		$ 100,000,000
Authorized value of common stock remaining for sale under agreement | $						$ 43,900,000
Series B Junior Participating Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares authorized (shares)						1,500,000.0	1,500,000			1,500,000.0
Preferred stock issued (shares)						0	0
Convertible preferred stock outstanding (shares)						0	0
Series E Convertible Voting Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares authorized (shares)						2,000	2,000
Cash proceeds from exchange of preferred stock | $					$ 20,000,000
Preferred stock issued (shares)					2,000	0	0
Preferred stock converted into common stock (shares)			40,000		4,000,000
Convertible preferred stock outstanding (shares)						0	0
Converted (shares)			20
Dividends in arrears | $			$ 6,000
BlackRock, Inc. [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock outstanding, ownership percentage						15.90%