Investments - Summary of Net Investment Income (Detail) (USD $) In Thousands, unless otherwise specified	2 Months Ended	3 Months Ended						8 Months Ended	12 Months Ended	1 Months Ended	3 Months Ended	4 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2014	Apr. 30, 2013	Mar. 31, 2013	Apr. 30, 2013	Dec. 31, 2012
Successor [Member]
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities								$ 3,580	$ 6,713
Trading Securities, Realized Gain (Loss)								1,702	(487)
Fixed income securities								147,014	299,694
Short-term investments								1,528	3,092
Loans								306	529
Investment expense								(5,982)	(10,477)
Securities available-for-sale and short-term								142,866	292,838
Other investments								3,580	8,108
Total net investment income	26,196	66,471	83,581	80,093	70,801	68,124	52,126	146,446	300,946
Predecessor [Member]
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities												369	0
Trading Securities, Realized Gain (Loss)												0	0
Fixed income securities												118,097	386,385
Short-term investments												677	1,405
Loans												146	714
Investment expense												(2,549)	(5,602)
Securities available-for-sale and short-term												116,371	382,902
Other investments												369	0
Total net investment income										32,226	84,514	116,740	382,902
Gains (losses) on securities held as of reporting date [Member] | Successor [Member]
Investment [Line Items]
Other investments								1,878	7,200
Gains (losses) on securities held as of reporting date [Member] | Predecessor [Member]
Investment [Line Items]
Other investments												$ 369	$ 0