Revenue from Contracts with Customers - Capitalized Costs (Details) - Contract Acquisition And Fulfillment Costs [Member] - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018
Capitalized Contract Cost [Roll Forward]
Beginning balance	$ 39,955	$ 27,165
Capitalization of contract acquisition and fulfillment costs	10,067	8,921
Amortization of deferred contract acquisition and fulfillment costs	(6,896)	(4,391)
Ending balance	$ 43,126	$ 31,695

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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-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

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