Significant Accounting Policies - Doubtful Accounts (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Schedule of allowance for doubtful accounts
Beginning allowance for doubtful accounts	$ 10,226	$ 8,688	$ 10,024	$ 8,835
Additions charged to expense	4,136	3,553	7,204	7,022
Write-offs, net of recoveries	(4,381)	(3,508)	(7,247)	(7,124)
Ending allowance for doubtful accounts	$ 9,981	$ 8,733	$ 9,981	$ 8,733