Income Taxes - Summary of Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Valuation Allowance [Abstract]
Balance at beginning of period	$ 77,756	$ 74,480	$ 64,545
Additions	928	9,028	18,291
Deductions	(1,540)	(5,752)	(8,356)
Balance at end of period	$ 77,144	$ 77,756	$ 74,480

Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319

Name:	us-gaap_DeferredTaxAssetsValuationAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant