Debt (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Interest expense on convertible notes
Interest expense at coupon rate (6.0%)	$ 2,756	$ 5,726	$ 5,850
Non-cash interest in accordance with ASC 470-20	5,450	10,538	8,149
Total interest expense recognized on convertible debt instruments	$ 8,206	$ 16,264	$ 13,999