Interest Expense Related to Convertible Notes (Detail) - Senior Notes - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule Of Interest Expenses [Line Items]
Contractual interest expense	$ 1,813	$ 1,812	$ 5,438	$ 2,074
Amortization of debt discount	2,058	1,872	6,032	2,141
Amortization of debt issuance costs	36	33	105	38
Total interest expense	$ 3,907	$ 3,717	$ 11,575	$ 4,253