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Commitments and Contingencies - Lease Commitments (Details) ft² in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Jan. 31, 2018 USD ($) ft²
Property, Plant and Equipment [Line Items] |  |  |  |
Operating lease rent expense | $ 4,700,000 | $ 3,900,000 | $ 3,700,000 |
Capital leased assets | 37,274,000 | 38,350,000 |  |
COLORADO | Subsequent event |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
New lease agreement, area of property (in square feet) | ft² |  |  |  | 30
Aggregate annual payment under new lease |  |  |  | $ 1,000,000.0
Computer Equipment and Furniture |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Capital leased assets | $ 0 | $ 0 | $ 500,000 |

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- Definition Amount before accumulated depreciation of leased physical assets used in the normal conduct of business to produce goods and services. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=84164758&loc=d3e45014-112735 + Details
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