Contractual Coupon Interest Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Contractual coupon interest expense	$ 5,063	$ 5,063	$ 5,063
Accretion of discount on the liability component	$ 4,256	$ 3,973	$ 3,710