Investments - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended
	Apr. 30, 2013	Sep. 30, 2019	Dec. 31, 2018
Investment [Line Items]
Fresh-Start Balance Sheet, Fresh-Start Balance Sheet Date	Apr. 30, 2013
Other investments		$ 462,427	$ 391,217
Securities fair value		6,281	5,975
Ambac Assurance [Member]
Investment [Line Items]
Unsettled Amounts Secured Notes from LSNI		12,561	19,405
Ambac UK [Member]
Investment [Line Items]
Asset Backed Securities Fair Value Disclosure		0	144,672
Interest Rate Contract [Member]
Investment [Line Items]
Other investments		234,758	177,357
Reported Value Measurement [Member] | Interest Rate Contract [Member]
Investment [Line Items]
Other investments		50,342	$ 27,154
Commitments [Member] | Partnership Interest [Member]
Investment [Line Items]
Other investments		9,827
Commitments [Member] | Capital of Dislocations [Member]
Investment [Line Items]
Other investments		$ 50,000