Debt (Tables)

3 Months Ended

Mar. 31, 2013

Debt [Abstract]

Summary of Convertible Notes and the equity component

	March 31,			December 31,
	2013			2012
	(in thousands)
Principal amount	$	143,750		$	143,750
Unamortized discount		(41,808	)		(43,435	)
Net carrying amount	$	101,942		$	100,315
Equity component	$	55,038		$	55,038

Summary of interest expense related to the Convertible Notes

	Three Months Ended March 31
	2013		2012
	(in thousands)
Stated amount at 3.5% coupon rate	$	1,258	$	1,258
Amortization of discount		1,626		1,442
Amortization of deferred financing costs		87		77
	$	2,971	$	2,777