Fair Value of Financial Instruments - Fair Value of Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes	$ 360,000	$ 360,000
Senior Notes [Member] | Significant Other Observable Inputs (Level 2) [Member] | 2011 Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stated interest rate	8.25%
Senior Notes [Member] | Significant Other Observable Inputs (Level 2) [Member] | 2012 Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stated interest rate	8.00%
Senior Notes [Member] | Significant Other Observable Inputs (Level 2) [Member] | 2013 Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stated interest rate	7.75%
Senior Notes [Member] | Carrying Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | 2011 Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes	$ 107,500	107,500
Senior Notes [Member] | Carrying Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | 2012 Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes	100,000	100,000
Senior Notes [Member] | Carrying Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | 2013 Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes	152,500	152,500
Senior Notes [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | 2011 Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes	113,219	113,391
Senior Notes [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | 2012 Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes	106,240	106,320
Senior Notes [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | 2013 Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes	$ 164,029	$ 162,016