Investments - Summary of Net Investment Income (Detail) - Successor [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	$ 3,000	$ 5,240
Trading Securities, Realized Gain (Loss)	2,070	1,498
Fixed income securities	81,751	66,104	$ 155,820	$ 125,527
Short-term investments	1,151	374	2,140	930
Loans	85	70	174	176
Investment expense	(2,044)	(2,180)	(4,041)	(4,283)
Securities available-for-sale and short-term	80,943	64,368	154,093	122,350
Other investments	4,217	6,390	12,626	9,229
Total net investment income	85,160	70,758	166,719	131,579
Gains (losses) on securities held as of reporting date [Member]
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities			10,211	6,948
Trading Securities, Realized Gain (Loss)			3,698	1,531
Other investments	$ 930	$ 3,742	$ 6,513	$ 5,417