Details of Two Point Five Zero Percent Convertible Notes Reflected on Consolidated Balance Sheet (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Debt Instrument [Line Items]
Net debt carrying amount	$ 1,486,312		$ 1,394,077
2.50% Convertible Notes
Debt Instrument [Line Items]
Equity component carrying amount	35,996		35,996
Unamortized discount	16,551		19,896
Net debt carrying amount	$ 283,449	[1]	$ 280,104

[1] Reflects the net debt carrying amount of the 2.50% Convertible Notes in the consolidated balance sheet as of March 31, 2015, in accordance with accounting for convertible notes. The principal amount owed to the holders of the 2.50% Convertible Notes is $300.0 million.