Investments - Summary of Net Investment Income (Detail) - Successor [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	$ (1,579)	$ 7,211
Trading Securities, Realized Gain (Loss)	1,933	1,283
Fixed income securities	109,351	74,069
Short-term investments	2,840	989
Loans	187	89
Investment expense	(1,827)	(1,997)
Securities available-for-sale and short-term	110,551	73,150
Other investments	(311)	8,409
Total net investment income	110,240	81,559
Gains (losses) on securities held as of reporting date [Member]
Investment [Line Items]
Other investments	$ (3,512)	$ 5,928