Convertible Senior Notes Due 2017 - Interest Expense on Convertible Notes (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 Disclosure [Abstract]
Coupon interest expense	$ 1,698	$ 1,698	$ 5,094	$ 5,094
Non-cash amortization of debt discount	3,538	3,197	10,149	9,166
Non-cash amortization of debt issuance costs	299	270	858	775
Total	$ 5,535	$ 5,165	$ 16,101	$ 15,035