Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Student receivables, allowance for doubtful accounts, current	$ 26,331	$ 23,307
Property and equipment, accumulated depreciation	192,613	198,052
Intangible assets, amortization	1,400	1,400
Student receivables, allowance for doubtful accounts, non-current	$ 1,598	$ 1,529
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	85,658,822	85,173,686
Common stock, shares outstanding	70,102,909	69,772,910
Treasury stock, shares	15,555,913	15,400,776