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Summary of Significant Accounting Policies - New Accounting Pronouncements (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2018 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Jan. 01, 2019
Summary Of Significant Policies [Line Items] |  |  |  |  |
Loss on extinguishment of debt | $ 2,200 | $ 2,209 | $ 0 | $ 0 |
Scenario, Forecast | Accounting Standards Update 2016-02 | Minimum |  |  |  |  |
Summary Of Significant Policies [Line Items] |  |  |  |  |
Operating lease, liability |  |  |  |  | $ 44,000
Operating lease, right-of-use asset |  |  |  |  | 44,000
Scenario, Forecast | Accounting Standards Update 2016-02 | Maximum |  |  |  |  |
Summary Of Significant Policies [Line Items] |  |  |  |  |
Operating lease, liability |  |  |  |  | 49,000
Operating lease, right-of-use asset |  |  |  |  | $ 49,000

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- Definition Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 50 -Section 40 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=114001942&loc=d3e12355-112629 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 50 -Section 40 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=114001942&loc=d3e12317-112629 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585 + Details
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