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Schedule II - Condensed Financial Information of Registrant (Parent Company Only) - Condensed Balance Sheet (Parenthetical) (Detail) - USD ($) $ / shares in Units, $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016 | May 01, 2013 | Apr. 30, 2013
--- | --- | --- | --- | ---
Condensed Balance Sheet Statements, Captions [Line Items] |  |  |  |
Tolling Payment Payable to AFG | $ 30,496 | $ 28,691 |  |
Preferred stock, par value |  |  |  | $ 0.01
Preferred stock, shares authorized |  |  |  | 20,000,000
Common stock, par value |  |  |  | $ 0.01
Common stock, shares authorized |  |  |  | 130,000,000
Common stock, shares issued |  |  |  | 45,000,000
Successor [Member] |  |  |  |
Condensed Balance Sheet Statements, Captions [Line Items] |  |  |  |
Fixed income securities, amortized cost | $ 4,614,623 | $ 5,435,385 |  |
Preferred stock, par value | $ 0.01 | $ 0.01 |  |
Preferred stock, shares authorized | 20,000,000 | 20,000,000 |  |
Preferred stock, shares issued | 0 | 0 |  |
Preferred Stock, Shares Outstanding | 0 | 0 |  |
Common stock, par value | $ 0.01 | $ 0.01 | $ 0.01 |
Common stock, shares authorized | 130,000,000 | 130,000,000 |  |
Common stock, shares issued |  |  | 45,000,000 |
Parent Company [Member] |  |  |  |
Condensed Balance Sheet Statements, Captions [Line Items] |  |  |  |
Fixed income securities, amortized cost | $ 239,476 | $ 220,749 |  |
Preferred stock, par value | $ 0.01 | $ 0.01 |  |
Preferred stock, shares authorized | 20,000,000 | 20,000,000 |  |
Common stock, par value | $ 0.01 | $ 0.01 |  |
Common stock, shares authorized | 130,000,000 | 130,000,000 |  |
Parent Company [Member] | Successor [Member] |  |  |  |
Condensed Balance Sheet Statements, Captions [Line Items] |  |  |  |
Common stock, shares issued | 45,275,982 | 45,194,954 |  |
Common stock, shares outstanding | 45,275,982 | 45,194,954 |  |
Treasury stock, shares | 24,816 | 22,458 |  |

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- Definition This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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