Consolidated Statements of Income - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Revenue	$ 299,248,000	$ 313,139,000	$ 327,910,000
Costs and expenses:
Instructional costs and services	116,161,000	117,013,000	118,848,000
Selling and promotional	58,335,000	59,095,000	62,397,000
General and administrative	69,024,000	68,666,000	73,047,000
Loss on disposals of long-lived assets	2,093,000	5,970,000	817,000
Impairment of goodwill	0	4,735,000	0
Depreciation and amortization	18,776,000	19,384,000	20,520,000
Total costs and expenses	264,389,000	274,863,000	275,629,000
Income from operations before interest income and income taxes	34,859,000	38,276,000	52,281,000
Interest income, net	185,000	116,000	115,000
Income from operations before income taxes	35,044,000	38,392,000	52,396,000
Income tax expense	11,493,000	14,940,000	20,072,000
Equity investment income (loss)	(2,430,000)	703,000	90,000
Net income	$ 21,121,000	$ 24,155,000	$ 32,414,000
Net income per common share:
Basic (in dollars per share)	$ 1.30	$ 1.50	$ 1.94
Diluted (in dollars per share)	$ 1.29	$ 1.49	$ 1.93
Weighted average number of shares outstanding:
Basic (in shares)	16,236	16,068	16,676
Diluted (in shares)	16,380	16,214	16,798