Quarterly Results of Operations (Unaudited) - Summarizes the Unaudited Quarterly Results of Operations (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement [Abstract]
Net revenue	$ 244,663	$ 210,444	$ 191,279	$ 226,958	$ 215,954	$ 193,393	$ 174,726	$ 194,127	$ 873,344	$ 778,200	$ 691,055
Costs and expenses:
Instructional costs and services	102,100	91,748	84,599	94,654	92,427	83,180	75,357	78,687	373,101	329,651	288,791
Admissions advisory and related	32,062	28,814	28,866	29,544	29,361	27,506	27,372	28,333	119,286	112,572	108,567
Advertising	21,000	23,896	22,149	21,107	18,419	19,360	18,419	20,031	88,152	76,229	65,808
Marketing and promotional	2,383	2,127	2,108	2,242	1,978	1,827	1,788	1,694	8,860	7,287	7,439
General and administrative	10,260	13,430	8,809	10,720	10,634	12,536	9,534	9,396	43,219	42,100	39,635
Lease termination costs	160	3,363							3,523
Total costs and expenses	167,965	163,378	146,531	158,267	152,819	144,409	132,470	138,141	636,141	567,839	510,240
Operating income	76,698	47,066	44,748	68,691	63,135	48,984	42,256	55,986	237,203	210,361	180,815
Interest expense	(497)	(344)	(158)	(329)	(414)	(313)	(146)	(375)	(1,328)	(1,248)	(1,801)
Interest income and other	199	(2,291)	293	2,048	(691)	201	127	257	249	(106)	684
Income before income taxes	76,400	44,431	44,883	70,410	62,030	48,872	42,237	55,868	236,124	209,007	179,698
Income tax expense	28,421	15,187	17,257	26,745	23,916	15,530	16,461	21,689	87,610	77,596	68,232
Net income	$ 47,979	$ 29,244	$ 27,626	$ 43,665	$ 38,114	$ 33,342	$ 25,776	$ 34,179	$ 148,514	$ 131,411	$ 111,466
Earnings per share:
Basic income per share	$ 1.03	$ 0.63	$ 0.60	$ 0.96	$ 0.83	$ 0.72	$ 0.56	$ 0.75	$ 3.22	$ 2.86	$ 2.45
Diluted income per share	$ 1.01	$ 0.62	$ 0.59	$ 0.93	$ 0.81	$ 0.70	$ 0.55	$ 0.72	$ 3.15	$ 2.78	$ 2.37
Basic weighted average shares outstanding	46,470	46,231	46,004	45,622	46,035	46,063	46,012	45,789	46,083	45,975	45,538
Diluted weighted average shares outstanding	47,452	47,175	46,990	46,860	47,337	47,320	47,263	47,201	47,121	47,281	47,006