Equity Compensation Plans - Stock-Based Compensation Expense and Related Income Tax Benefit (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 10,336	$ 11,638	$ 16,658
Income tax (benefit)	(3,980)	(4,481)	(6,414)
Cost of Educational Services [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	4,790	4,799	6,084
Student Services and Administrative Expenses [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 5,546	$ 6,839	$ 10,574