Net Carrying Amount of Debt (Parenthetical) (Detail)	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Mar. 18, 2013	May. 23, 2011
1.50% Convertible Notes
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	1.50%	1.50%	1.50%	1.50%	1.50%	1.50%
2.50% Convertible Notes
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.50%	2.50%	2.50%	2.50%	2.50%		2.50%