Investments - Summary of Net Investment Income (Detail) - Successor [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	$ 3,632	$ 3,000
Trading Securities, Realized Gain (Loss)	344	2,070
Fixed income securities	60,499	81,751	$ 169,848	$ 155,820
Short-term investments	2,438	1,151	5,278	2,140
Loans	179	85	367	174
Investment expense	(1,374)	(2,044)	(3,200)	(4,041)
Securities available-for-sale and short-term	61,742	80,943	172,293	154,093
Other investments	4,920	4,217	4,609	12,626
Total net investment income	66,662	85,160	176,902	166,719
Gains (losses) on securities held as of reporting date [Member]
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities			2,053	10,211
Trading Securities, Realized Gain (Loss)			1,325	3,698
Other investments	$ 3,288	$ 930	$ 728	$ 6,513