Principal Balance Unamortized Discount and Net Carrying Amount (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Liability component, principal balance	$ 293,382	$ 293,382
Liability component, unamortized discount	57,651	70,468
Liability component, net carrying amount	235,731	222,914
Senior Notes Due 2019
Debt Instrument [Line Items]
Liability component, principal balance	170,941	170,941
Liability component, unamortized discount	35,283	45,114
Liability component, net carrying amount	135,658	125,827
Senior Convertible Notes Due 2018
Debt Instrument [Line Items]
Liability component, principal balance	122,441	122,441
Liability component, unamortized discount	22,368	25,354
Liability component, net carrying amount	$ 100,073	$ 97,087