Company's Debt Maturities on Calendar Year Basis (Parenthetical) (Detail) - Convertible Notes - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Mar. 18, 2013	May. 23, 2011
1.50% Senior Subordinated Notes Due March 15, 2018
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	1.50%	1.50%	1.50%	1.50%
Principal amount of long term debt	$ 400.0			$ 400.0
2.50% Senior Subordinated Notes Due June 2016
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.50%	2.50%	2.50%		2.50%
Principal amount of long term debt	$ 300.0				$ 300.0