Schedule of Debt Obligations (Parenthetical) (Detail) - Convertible Notes - 1.50% Senior Subordinated Notes Due March 15, 2018 - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jul. 31, 2016	Jun. 30, 2016	Mar. 31, 2016	Mar. 18, 2013	May 23, 2011
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	1.50%	1.50%				1.50%	1.50%	2.50%
Debt instrument, par value of notes repurchased	$ 104.9		$ 104.9	$ 53.2	$ 51.7