Convertible Senior Notes Due 2017 - Interest Expense on Convertible Notes (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Debt Disclosure [Abstract]
Coupon interest expense	$ 1,698	$ 1,698	$ 3,396	$ 3,396
Non-cash amortization of debt discount	3,355	3,028	6,611	5,969
Non-cash amortization of debt issuance costs	283	256	559	505
Total	$ 5,336	$ 4,982	$ 10,566	$ 9,870