Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accounting Policies [Abstract]
Advertising costs	$ 14,992	$ 14,416	$ 27,829	$ 27,497
Internal-use software development costs	$ 7,864	$ 1,812	$ 12,900	$ 2,267

The cash outflow associated with the development or modification of software programs or applications for internal use (that is, not to be sold, leased or otherwise marketed to others) that qualify for capitalization.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3213-108585

Name:	us-gaap_PaymentsToDevelopSoftware
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration