Summary of Significant Accounting Policies - Schedule of Changes in Allowance for Doubtful Accounts and Sales Allowances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Review period for past due accounts	90 days
Allowance for Doubtful Accounts
Allowances, at beginning of period	$ 2,600	$ 2,720	$ 2,069
Charged as a reduction of revenue	7,734	7,042	6,716
Charged to bad debt expense in general and administrative expenses	1,385	1,285	925
Write-offs, net of recoveries	(8,689)	(8,447)	(6,990)
Allowances, at end of period	$ 3,030	$ 2,600	$ 2,720