Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Student receivables, allowance for doubtful accounts, current	$ 19,304	$ 18,013
Student receivables, allowance for doubtful accounts, non-current	$ 1,754	$ 2,216
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	83,509,840	82,996,585
Common stock, shares outstanding	68,492,083	68,098,654
Treasury, Shares in treasury	15,017,757	14,897,931