Insurance Operations - Summary of Reconciliations of Direct to Net premiums on Written and Earned Basis Related to Wholly Owned Insurance Company Subsidiary (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Premiums Written and Earned [Abstract]
Written, Direct	$ 71.8	$ 71.5	$ 34.9
Written, Assumed	5.2	4.4	2.3
Written, Ceded	(77.0)	(75.9)	(37.2)
Written, Net	0.0	0.0	0.0
Earned, Direct	69.6	71.7	2.4
Earned, Assumed	4.9	5.1	0.2
Earned, Ceded	(74.5)	(76.8)	(2.6)
Earned, Net	$ 0.0	$ 0.0	$ 0.0