Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 9,183	$ 10,298	$ 10,017
Charged to cost and expenses	184	(245)	692
Write-offs (recoveries) of doubtful accounts	1,117	870	411
Balance at end of period	8,250	9,183	10,298
Student Loan [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	15,682	8,622	17,603
Charged to cost and expenses	15,917	19,019	12,595
Write-offs (recoveries) of doubtful accounts	10,573	11,959	21,576
Balance at end of period	$ 21,026	$ 15,682	$ 8,622