Significant Accounting Policies (Details 5) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2014 2 3/4 percent convertible senior notes [Member]	Dec. 31, 2013 2 3/4 percent convertible senior notes [Member]	Aug. 31, 2012 2 3/4 percent convertible senior notes [Member]	Sep. 30, 2012 2 5/8 percent convertible subordinated notes
Long-term obligations
Interest rate on convertible debt (in hundredths)	2.75%	2.75%	2.75%	2.75%		2.625%
Debt issued					$ 201.3