Net Income (Loss) Per Common Share - Calculation of Diluted Net Income (Loss) Per Share Attributable to Common Stockholders (Parenthetical) (Details) - shares	12 Months Ended
Dec. 31, 2017	Dec. 31, 2015
Earnings Per Share [Abstract]
Dilutive effects from equity instruments	0	0

Additional shared included in the calculation of diluted EPS as a result of the potentially dilutive effect of equity forward arrangements using the reverse treasury stock method.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=96947427&loc=d3e2366-109256

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Name:	us-gaap_IncrementalCommonSharesAttributableToEquityForwardAgreements
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration