Summary of Significant Accounting Policies - Deferred Contract Acquisition and Fulfillment Costs (Details) - Contract Acquisition And Fulfillment Costs [Member] $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($)
Capitalized Contract Cost [Roll Forward]
Beginning balance	$ 27,165
Capitalization of contract acquisition and fulfillment costs	22,765
Amortization of deferred contract acquisition and fulfillment costs	(9,975)
Ending balance	$ 39,955

Amount, after accumulated amortization and accumulated impairment loss, of asset recognized from cost incurred to obtain or fulfill contract with customer.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=68051541&loc=SL49131252-203054

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant