Legal and Regulatory Matters - Brazilian Regulation (Details) - Brazil $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) educational_institution	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Loss Contingencies [Line Items]
Number of postsecondary educational institutions (educational institution) | educational_institution	13
Percentage of students enrolled in government programs	16.00%
Percentage of funds received	24.00%
Revenue from grants | $	$ 115,200	$ 83,900	$ 55,000