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

X

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
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+ References

No definition available.

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=6526789

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