Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Student receivables, allowance for doubtful accounts, current	$ 21,571	$ 20,533
Property and equipment, accumulated depreciation	195,650	213,825
Intangible assets, amortization	1,400	1,400
Student receivables, allowance for doubtful accounts, non-current	$ 1,980	$ 2,001
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	1,000,000	1,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	85,159,221	84,279,533
Common stock, shares outstanding	69,760,992	69,117,803
Treasury stock, Shares	15,398,229	15,161,730