Stock-Based Compensation - Summary of Stock-based Compensation Cost Charged Against Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense in operating income	$ 1,502	$ 1,394
Tax benefit	(595)	(574)
Stock-based compensation expense, net of tax	907	820
Instructional costs and services
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense in operating income	430	384
Selling and promotional
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense in operating income	184	165
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense in operating income	$ 888	$ 845