v3.8.0.1

Fair Value of Financial Instruments - Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands | Sep. 30, 2017 | Dec. 31, 2016
--- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Other investments, at fair value (cost 2017: $5,640; 2016: $10,057) | $ 7,041 | $ 13,060
Financial Assets | 5,043,734 | 4,750,861
Carrying Value [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Liabilities | 262,500 | 362,500
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Liabilities | 276,640 | 377,752
Senior Notes [Member] | Carrying Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | MHLA - 6.625% [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Liabilities | $ 110,000 | $ 110,000
Stated interest rate | 6.625% | 6.625%
Senior Notes [Member] | Carrying Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | MHNC - 7.75% [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Liabilities | $ 152,500 | $ 152,500
Stated interest rate | 7.75% | 7.75%
Senior Notes [Member] | Carrying Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | MHNB - 8.00% [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Liabilities | $ 0 | $ 100,000
Stated interest rate |  | 8.00%
Senior Notes [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | MHLA - 6.625% [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Liabilities | 117,040 | $ 111,452
Senior Notes [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | MHNC - 7.75% [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Liabilities | 159,600 | 164,700
Senior Notes [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | MHNB - 8.00% [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Liabilities | 0 | 101,600
Held-to-maturity securities [Member] | Carrying Value [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Assets | 1,118,368 | 752,212
Held-to-maturity securities [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Assets | 1,152,106 | 766,135
Corporate bonds [Member] | Held-to-maturity securities [Member] | Carrying Value [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Assets | 1,057,943 | 752,212
Corporate bonds [Member] | Held-to-maturity securities [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Assets | 1,091,222 | 766,135
Municipal bonds [Member] | Held-to-maturity securities [Member] | Carrying Value [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Assets | 60,425 | 0
Municipal bonds [Member] | Held-to-maturity securities [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Assets | $ 60,884 | $ 0

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