Investments - Summary of Net Investment Income (Detail) - Successor [Member] - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities									$ 27,654	$ 12,615	$ 6,713
Trading Securities, Realized Gain (Loss)									7,474	4,966	(487)
Fixed income securities									288,554	257,404	299,694
Short-term investments									1,505	299	3,092
Loans									337	420	529
Investment expense									(9,347)	(8,786)	(10,477)
Securities available-for-sale and short-term									281,049	249,337	292,838
Other investments									32,318	16,952	8,108
Total net investment income	$ 90,871	$ 90,917	$ 70,758	$ 60,821	$ 64,358	$ 64,195	$ 64,753	$ 72,983	313,367	266,289	300,946
Gains (losses) on securities held as of reporting date [Member]
Investment [Line Items]
Other investments									$ 20,180	$ 7,649	$ 7,200