Contractual Coupon Interest Expense (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Debt Instrument [Line Items]
Contractual coupon interest expense	$ 1,266	$ 1,266	$ 3,797	$ 3,797
Accretion of discount on the liability component	$ 1,002	$ 935	$ 2,954	$ 2,759