Business Combinations - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Apr. 05, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Goodwill	$ 781,972		$ 615,433
Community Education Centers
Business Acquisition [Line Items]
Accounts Receivable		$ 29,916
Prepaid and other current assets		4,407
Property and equipment		126,510
Intangible assets		76,000
Favorable lease assets		3,110
Deferred income tax assets		1,792
Other non-current assets		4,327
Total assets acquired		246,062
Accounts payable and accrued expenses		52,341
Unfavorable lease liabilities		1,299
Other non-current liabilities		5,360
Total liabilities assumed		59,000
Total identifiable net assets		187,062
Goodwill		166,493
Total consideration paid, net of cash acquired		$ 353,555