Senior Notes - 7.50% Senior Convertible Notes and 7.50% Senior Exchange Convertible Notes due 2016 (Details) - USD ($) $ in Millions	Jul. 20, 2015	Sep. 30, 2016	Dec. 31, 2015	Jun. 23, 2015	Jul. 31, 2012	Feb. 04, 2011
7.50% Senior Convertible Notes due 2016
Debt
Stated interest rate (percent)		7.50%	7.50%
Senior Notes | 7.50% Senior Convertible Notes due 2016
Debt
Stated interest rate (percent)						7.50%
Aggregate principal amount						$ 100.0
Face amount of debt retired				$ 8.7	$ 44.5
Senior Notes | 7.50% Senior Exchange Convertible 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%