Income Taxes - Reconciliation of Income Tax Expense (Parenthetical) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation Allowance [Line Items]
Computed income tax expense at statutory federal income tax rate of 35%, tax rate	35.00%	35.00%	35.00%
Increase to valuation allowance related to remeasurement of deferred taxes due to reduction in U.S. tax rate	$ (796)	$ 1,230	$ (944)
U.S
Valuation Allowance [Line Items]
Increase to valuation allowance related to remeasurement of deferred taxes due to reduction in U.S. tax rate	$ 600

Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to increase (decrease) in the valuation allowance for deferred tax assets.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32698-109319

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=84176650&loc=d3e32123-109318

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration