Fair Value Measurements - Fair Value of Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 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
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior Subordinated Debt	0	152,500
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	113,090	101,480
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	105,400	89,760
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	159,826	126,209
Carrying Value [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior Subordinated Debt	0	126,381
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
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
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] | 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%
Junior Subordinated Debt [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stated interest rate	14.00%