Senior Notes - 7.50% Senior Convertible Notes and 7.50% Senior Exchange Convertible Notes due 2016 (Details) - USD ($) $ in Millions	Jul. 20, 2015	Mar. 31, 2016	Dec. 31, 2015	Jun. 23, 2015	Mar. 31, 2015	Jul. 31, 2012	Feb. 04, 2011
7.50% Senior Convertible Notes (the "7.50% Notes")
Debt
Stated interest rate (percent)		7.50%	7.50%		7.50%		7.50%
Aggregate principal amount							$ 100.0
Face amount of debt retired				$ 8.7		$ 44.5
7.50% Senior Exchange Convertible Notes due 2016 (“7.50% Exchange Notes”)
Debt
Stated interest rate (percent)							7.50%
Aggregate principal amount						$ 44.5
Face amount of debt retired				$ 20.5
Redemption price as a percentage of principal	100.00%