Fair Value Measurements - Fair Value of Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes	$ 360,000	$ 360,000
Junior subordinated debt	0	126,381
Senior notes | Significant Other Observable Inputs (Level 2) | 2011 Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stated interest rate	8.25%
Senior notes | Significant Other Observable Inputs (Level 2) | 2012 Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stated interest rate	8.00%
Senior notes | Significant Other Observable Inputs (Level 2) | 2013 Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stated interest rate	7.75%
Junior subordinated debt | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stated interest rate	14.00%
Carrying Value | Senior notes | Significant Other Observable Inputs (Level 2) | 2011 Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes	107,500	107,500
Carrying Value | Senior notes | Significant Other Observable Inputs (Level 2) | 2012 Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes	100,000	100,000
Carrying Value | Senior notes | Significant Other Observable Inputs (Level 2) | 2013 Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes	152,500	152,500
Carrying Value | Junior subordinated debt | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt	0	126,381
Fair Value | Senior notes | Significant Other Observable Inputs (Level 2) | 2011 Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes	113,391	101,480
Fair Value | Senior notes | Significant Other Observable Inputs (Level 2) | 2012 Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes	106,320	89,760
Fair Value | Senior notes | Significant Other Observable Inputs (Level 2) | 2013 Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes	162,016	126,209
Fair Value | Junior subordinated debt | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt	$ 0	$ 152,500