Summary of Significant Accounting Policies - Revenue - Amortization Expense Associated with Commissions Asset and Intake Costs (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2018
Commissions asset
Capitalized Contract Cost [Line Items]
Amortization expense	$ 3,793	$ 7,380
Intake Costs asset
Capitalized Contract Cost [Line Items]
Amortization expense	$ 2,891	$ 5,621

Amount of amortization expense for 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 (b)
-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:	duration