Comprehensive Income - Schedule of Amounts Reclassed Out of Each Component of Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	4 Months Ended	12 Months Ended	8 Months Ended	12 Months Ended
	Apr. 30, 2013	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2014
Predecessor [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense (benefit)	$ (755)	$ (2,849)
Predecessor [Member] | Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized investment gains	(12,865)
Net of tax and noncontrolling interest	(12,865)
Predecessor [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax and noncontrolling interest	(12,680)
Predecessor [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense (benefit)	0
Predecessor [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense (benefit)	(704)
Prior service cost	1,616
Actuarial gains (losses)	(727)
Total before tax	889
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	185
Successor [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense (benefit)			(7,514)	(9,557)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(12,680)		43,731	(33,778)
Successor [Member] | Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized investment gains			43,731	(32,962)
Net of tax and noncontrolling interest			43,731	(32,962)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(12,865)		43,731	(32,962)
Successor [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	185		0	(816)
Successor [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax and noncontrolling interest			43,731	(33,778)
Successor [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Prior service cost			0	(664)
Actuarial gains (losses)			0	(152)
Total before tax			0	(816)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			$ 0	$ (816)