Summary of Significant Accounting Policies - Revenue - Contract Fulfillment Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018
Commissions asset
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net Carrying Amount	$ 20,478
Accumulated Amortization	(28,355)	$ (21,173)
Gross Carrying Amount	48,833	42,072
Intake Costs asset
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net Carrying Amount	15,508
Accumulated Amortization	(20,135)	(14,954)
Gross Carrying Amount	$ 35,643	31,604
Accounting Standards Update 2014-09 \| Commissions asset
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net Carrying Amount		20,899
Accounting Standards Update 2014-09 \| Intake Costs asset
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net Carrying Amount		$ 16,650

Amount, before allowance for credit loss, of right to consideration in exchange for good or service transferred to customer, when right is conditioned on something other than passage of time.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82913815&loc=SL49130531-203044

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130549-203045

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=82913815&loc=SL49130533-203044

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