Consolidated Balance Sheets (Parenthetical) - Successor [Member] - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fixed income securities, amortized cost	$ 3,355,223	$ 4,614,623
Fixed income securities pledged as collateral, amortized cost	84,641	99,719
Short-term investments, amortized cost	$ 393,516	$ 557,476
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred stock, shares issued	0	0
Preferred Stock, Shares Outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	130,000,000	130,000,000
Common stock, shares outstanding	45,332,214
Equity investments in pooled funds [Member]
Other Investments at Fair Value	$ 356,899	$ 396,689
Parent Company [Member]
Common stock, shares issued	45,365,170	45,275,982
Common stock, shares outstanding	45,365,170	45,275,982
Treasury stock, shares	32,956	24,816