Income Taxes - Valuation Allowances and Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Income Taxes
Amount of decrease in valuation allowance	$ 5,000
Valuation allowance		$ 4,993
Unrecognized tax benefits	0	$ 2,100
Decrease in unrecognized tax benefits, expiration of statute of limitations	$ 2,100

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

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
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-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319

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- References

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- Definition

Amount of unrecognized tax benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 10B
-URI http://asc.fasb.org/extlink&oid=84176650&loc=SL37586934-109318

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Section 50
-Paragraph 15A
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- Definition

Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
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-URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319

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- Definition

Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 20
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