Comprehensive Income - Schedule of Changes in Balances of Each Component of Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	4 Months Ended	8 Months Ended	12 Months Ended
	Apr. 30, 2013	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2012
Predecessor [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance				$ 625,385
Ending Balance	800,260			625,385
Successor [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance		0	11,661
Other comprehensive income before reclassifications	187,555	(32,070)	242,400
Amounts reclassified from accumulated other comprehensive income	(12,680)	43,731	(33,778)
Elimination Of Predecessor Shareholder Equity And Noncontrolling Interest	(800,260)
Net current period other comprehensive income	(625,385)	11,661	208,622
Ending Balance	0	11,661	220,283
Unrealized Gains (Losses) on Available-for-Sale Securities [Member] | Predecessor [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance				651,272
Ending Balance				651,272
Unrealized Gains (Losses) on Available-for-Sale Securities [Member] | Successor [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance		0	(41,910)
Other comprehensive income before reclassifications	188,212	(85,641)	285,565
Amounts reclassified from accumulated other comprehensive income	(12,865)	43,731	(32,962)
Elimination Of Predecessor Shareholder Equity And Noncontrolling Interest	(826,619)
Net current period other comprehensive income	(651,272)	(41,910)	252,603
Ending Balance		(41,910)	210,693
Other Postretirement Benefit Plan, Defined Benefit [Member] | Predecessor [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance				(5,860)
Ending Balance				(5,860)
Other Postretirement Benefit Plan, Defined Benefit [Member] | Successor [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance		0	10,847
Other comprehensive income before reclassifications	0	10,847	0
Amounts reclassified from accumulated other comprehensive income	185	0	(816)
Elimination Of Predecessor Shareholder Equity And Noncontrolling Interest	5,675
Net current period other comprehensive income	5,860	10,847	(816)
Ending Balance		10,847	10,031
Accumulated Translation Adjustment [Member] | Predecessor [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance				(20,027)
Ending Balance				(20,027)
Accumulated Translation Adjustment [Member] | Successor [Member]
Changes In Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance		0	42,724
Other comprehensive income before reclassifications	(657)	42,724	(43,165)
Amounts reclassified from accumulated other comprehensive income	0	0	0
Elimination Of Predecessor Shareholder Equity And Noncontrolling Interest	20,684
Net current period other comprehensive income	20,027	42,724	(43,165)
Ending Balance		$ 42,724	$ (441)