Investments - Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Investments, Excluding VIE Investments (Detail) - Successor [Member] - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 6,041,185	$ 5,283,157
Gross Unrealized Gains	187,585	155,169
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	76,831	104,206
Estimated Fair Value	6,151,939	5,334,120
Non - credit other - than - temporary Impairments	43,928	41,673
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	2,622,724	2,588,556
Short-Term [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	436,759	225,789
Gross Unrealized Gains	1	1
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	1
Estimated Fair Value	436,760	225,789
Non - credit other - than - temporary Impairments	0	0
Fixed Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,539,759	4,992,756
Gross Unrealized Gains	187,333	155,168
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	76,831	104,148
Estimated Fair Value	5,650,261	5,043,776
Non - credit other - than - temporary Impairments	43,928	41,673
Fixed Income Securities [Member] \| Securities Pledged as Collateral [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	64,667	64,612
Gross Unrealized Gains	251	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	57
Estimated Fair Value	64,918	64,555
Non - credit other - than - temporary Impairments	0	0
Fixed Income Securities [Member] \| Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	380,190	424,048
Gross Unrealized Gains	10,609	4,910
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	4,969	8,188
Estimated Fair Value	385,830	420,770
Non - credit other - than - temporary Impairments	0	0
Fixed Income Securities [Member] \| Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,626,276	1,610,912
Gross Unrealized Gains	27,929	7,089
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	7,901	24,332
Estimated Fair Value	1,646,304	1,593,669
Non - credit other - than - temporary Impairments	0	0
Fixed Income Securities [Member] \| Foreign Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	92,596	96,638
Gross Unrealized Gains	4,106	1,491
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	61	1,823
Estimated Fair Value	96,641	96,306
Non - credit other - than - temporary Impairments	0	0
Fixed Income Securities [Member] \| U.S. Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	32,185	26,086
Gross Unrealized Gains	1,357	789
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	93	188
Estimated Fair Value	33,449	26,687
Non - credit other - than - temporary Impairments	0	0
Fixed Income Securities [Member] \| U.S. Government Obligations [Member] \| Securities Pledged as Collateral [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	64,667	64,612
Gross Unrealized Gains	251	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	57
Estimated Fair Value	64,918	64,555
Non - credit other - than - temporary Impairments	0	0
Fixed Income Securities [Member] \| U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,195	4,239
Gross Unrealized Gains	0	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	9	27
Estimated Fair Value	4,186	4,212
Non - credit other - than - temporary Impairments	0	0
Fixed Income Securities [Member] \| Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,229,764	1,942,285
Gross Unrealized Gains	103,842	99,670
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	59,551	64,617
Estimated Fair Value	2,274,055	1,977,338
Non - credit other - than - temporary Impairments	43,928	41,673
Fixed Income Securities [Member] \| Collateralized Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	100,949	85,706
Gross Unrealized Gains	59	42
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	1,667	1,481
Estimated Fair Value	99,341	84,267
Non - credit other - than - temporary Impairments	0	0
Fixed Income Securities [Member] \| Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,073,604	802,842
Gross Unrealized Gains	39,431	41,177
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	2,580	3,492
Estimated Fair Value	1,110,455	840,527
Non - credit other - than - temporary Impairments	0	0
Fixed Income Investments And Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,976,518	5,218,545
Gross Unrealized Gains	187,334	155,169
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	76,831	104,149
Estimated Fair Value	6,087,021	5,269,565
Non - credit other - than - temporary Impairments	$ 43,928	$ 41,673

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
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-Publisher FASB
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
-Paragraph 2
-Subparagraph (c)
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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