Insurance Operations - Summary of Reconciliations of Direct to Net premiums on Written and Earned Basis Related to Wholly Owned Underwriting Enterprise Subsidiary (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Premiums Written and Earned [Abstract]
Written, Direct	$ 44.6	$ 57.6	$ 60.7
Written, Assumed	1.0	4.7	5.0
Written, Ceded	(45.6)	(62.3)	(65.7)
Written, Net	0.0	0.0	0.0
Earned, Direct	59.1	53.2	60.4
Earned, Assumed	1.9	4.6	4.5
Earned, Ceded	(61.0)	(57.8)	(64.9)
Earned, Net	$ 0.0	$ 0.0	$ 0.0