Investments - Summary of Net Investment Income (Detail) - Successor [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	$ 7,211	$ 1,707
Trading Securities, Realized Gain (Loss)	1,283	406
Fixed income securities	74,069	59,426
Short-term investments	989	553
Loans	89	106
Investment expense	(1,997)	(2,103)
Securities available-for-sale and short-term	73,150	57,982
Other investments	8,409	2,839
Total net investment income	81,559	60,821
Gains (losses) on securities held as of reporting date [Member]
Investment [Line Items]
Other investments	$ 5,928	$ 1,301