Segment Reporting - Summary Financial Information by Reporting Segment (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended					12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Settlement reserve						$ 7.1
Significant legal settlements charge	$ 7.1	$ 30.0	$ 5.0	$ 6.0	$ 3.5
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Significant legal settlements charge						7.1	$ 14.6	$ 6.5
Charge related to remaining lease obligations							$ 9.4	$ 14.8
CTU [Member]
Segment Reporting Information [Line Items]
Settlement reserve						18.6
AIU [Member]
Segment Reporting Information [Line Items]
Settlement reserve						$ 11.4