Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Allowance for doubtful accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 229	$ 259	$ 436
(Release) Provision for Bad Debts	(79)	142	47
Net Write-offs	(94)	(172)	(224)
Balance at End of Year	56	229	259
Refund Reserve
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	396	282	487
(Release) Provision for Bad Debts	24,987	21,240	22,446
Net Write-offs	(24,829)	(21,126)	(22,651)
Balance at End of Year	$ 554	$ 396	$ 282