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Investments - Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Investments, Excluding VIE Investments (Detail) - Successor [Member] - USD ($) $ in Thousands | Dec. 31, 2015 | Dec. 31, 2014
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | $ 5,283,157 | $ 4,939,325
Gross Unrealized Gains | 155,169 | 242,962
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 104,206 | 32,269
Estimated Fair Value | 5,334,120 | 5,150,018
Non - credit other - than - temporary Impairments | 41,673 | 7,773
Corporate Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Estimated Fair Value | 2,588,556 | 2,743,050
Residential Mortgage-Backed Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 1,942,285 |
Estimated Fair Value | 1,977,338 |
Collateralized Debt Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 85,706 |
Estimated Fair Value | 84,267 |
Asset-backed Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 802,842 |
Estimated Fair Value | 840,527 |
Short-Term [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 225,789 | 360,069
Gross Unrealized Gains | 1 | 0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 1 | 4
Estimated Fair Value | 225,789 | 360,065
Non - credit other - than - temporary Impairments | 0 | 0
Fixed Income Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 4,992,756 | 4,514,878
Gross Unrealized Gains | 155,168 | 242,962
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 104,148 | 32,154
Estimated Fair Value | 5,043,776 | 4,725,686
Non - credit other - than - temporary Impairments | 41,673 | 7,773
Fixed Income Securities [Member] | Securities Pledged as Collateral [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 64,612 | 64,378
Gross Unrealized Gains | 0 | 0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 57 | 111
Estimated Fair Value | 64,555 | 64,267
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 | 424,048 | 523,019
Gross Unrealized Gains | 4,910 | 9,769
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 8,188 | 6,996
Estimated Fair Value | 420,770 | 525,792
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 | 1,610,912 | 1,382,195
Gross Unrealized Gains | 7,089 | 12,815
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 24,332 | 9,416
Estimated Fair Value | 1,593,669 | 1,385,594
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 | 96,638 | 126,041
Gross Unrealized Gains | 1,491 | 3,060
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 1,823 | 1,344
Estimated Fair Value | 96,306 | 127,757
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 | 26,086 | 42,328
Gross Unrealized Gains | 789 | 1,078
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 188 | 427
Estimated Fair Value | 26,687 | 42,979
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 | 64,612 | 64,378
Gross Unrealized Gains | 0 | 0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 57 | 111
Estimated Fair Value | 64,555 | 64,267
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 | 4,239 | 29,524
Gross Unrealized Gains | 0 | 0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 27 | 38
Estimated Fair Value | 4,212 | 29,486
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 | 1,942,285 | 1,557,059
Gross Unrealized Gains | 99,670 | 167,396
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 64,617 | 13,500
Estimated Fair Value | 1,977,338 | 1,710,955
Non - credit other - than - temporary Impairments | 41,673 | 7,773
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 85,706 | 21,346
Gross Unrealized Gains | 42 | 50
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 1,481 | 274
Estimated Fair Value | 84,267 | 21,122
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 | 802,842 | 833,366
Gross Unrealized Gains | 41,177 | 48,794
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 3,492 | 159
Estimated Fair Value | 840,527 | 882,001
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 | 5,218,545 | 4,874,947
Gross Unrealized Gains | 155,169 | 242,962
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 104,149 | 32,158
Estimated Fair Value | 5,269,565 | 5,085,751
Non - credit other - than - temporary Impairments | $ 41,673 | $ 7,773

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