Fair Value of Assets and Liabilities (Details Textual) (Senior Notes)	Mar. 31, 2015	Dec. 31, 2014
5.875% Senior Notes, Due 2024
Debt Instrument [Line Items]
Interest rate	5.875%	5.875%
5.875% Senior Notes, Due 2022
Debt Instrument [Line Items]
Interest rate	5.875%	5.875%
7.75% Senior Notes
Debt Instrument [Line Items]
Interest rate	7.75%
6.625% Senior Notes, Due 2021
Debt Instrument [Line Items]
Interest rate	6.625%	6.625%
5.125% Senior Notes, Due 2023
Debt Instrument [Line Items]
Interest rate	5.125%	5.125%