Significant Accounting Policies - Doubtful Accounts (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Schedule of allowance for doubtful accounts
Allowance for doubtful accounts, beginning of period	$ 15,048	$ 11,760	$ 12,687	$ 10,201
Additions charged to expense	9,864	5,364	22,851	14,835
Additions from merger	6,601		6,601
Write-offs, net of recoveries	(6,118)	(4,567)	(16,744)	(12,479)
Allowance for doubtful accounts, end of period	$ 25,395	$ 12,557	$ 25,395	$ 12,557