Investments - Summary of Net Investment Income (Detail) - Successor [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	$ 4,919	$ 10,197
Trading Securities, Realized Gain (Loss)	5,024	1,859
Fixed income securities	81,054	81,831	$ 236,876	$ 207,358
Short-term investments	1,986	194	4,124	1,124
Loans	187	97	361	273
Investment expense	(2,228)	(2,592)	(6,269)	(6,875)
Securities available-for-sale and short-term	80,999	79,530	235,092	201,880
Other investments	6,178	11,387	18,804	20,616
Total net investment income	87,177	90,917	253,896	222,496
Gains (losses) on securities held as of reporting date [Member]
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities			15,130	17,145
Trading Securities, Realized Gain (Loss)			8,140	5,268
Other investments	$ (105)	$ 8,338	$ 6,990	$ 11,877