Significant Accounting Policies - Goodwill and Indefinite-Lived Intangible Assets (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Goodwill and Indefinite-Lived Intangible Assets
Balance as of the beginning of the period		$ 20,744,000	$ 6,800,000
Acquisition (see Note 3)			14,242,000
Measurement period adjustments			(298,000)
Balance as of the end of period	$ 20,744,000	20,744,000	20,744,000
New York Code And Design Academy, Inc.
Goodwill and Indefinite-Lived Intangible Assets
Balance as of the beginning of the period		$ 13,944,000
Balance as of the end of period			$ 13,944,000
Goodwill and intangible assets impairment	0
Jack Welch Management Institute
Goodwill and Indefinite-Lived Intangible Assets
Goodwill and intangible assets impairment	$ 0
Minimum
Long-Term Liabilities
Lease term		5 years
Maximum
Long-Term Liabilities
Lease term		10 years