Fair Value of Financial Instruments - Fair Value of Financial Instruments (Details) - Significant Other Observable Inputs (Level 2) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Assets	$ 0	$ 1,015,681
Financial Liabilities	262,500	262,500
Carrying Value \| Senior Notes \| Senior Notes - MHLA – 6.625%
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%
Carrying Value \| Senior Notes \| Senior Notes - MHNC – 7.75%
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%
Carrying Value \| Held-to-maturity securities \| Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Assets	$ 0	$ 957,845
Carrying Value \| Held-to-maturity securities \| Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Assets	0	57,836
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Assets	0	998,012
Financial Liabilities	212,130	219,200
Fair Value \| Senior Notes \| Senior Notes - MHLA – 6.625%
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities	78,540	75,240
Fair Value \| Senior Notes \| Senior Notes - MHNC – 7.75%
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities	133,590	143,960
Fair Value \| Held-to-maturity securities \| Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Assets	0	940,727
Fair Value \| Held-to-maturity securities \| Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Assets	$ 0	$ 57,285

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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+ References

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- Definition

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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
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