Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ (8.4)	$ 63.6	$ 50.3
Other comprehensive income (loss):
Foreign currency translation adjustments	(0.2)	(3.4)	(1.4)
Defined benefit pension plans:
Net (loss) gain arising during the year	(1.8)	1.2	1.2
Unrealized gains (losses) on securities:
Gains (losses) arising during the year	88.0	(93.9)	105.7
Reclassification adjustment for losses (gains) included in net income	9.9	5.4	(41.6)
Other comprehensive income (loss) before tax	95.9	(90.7)	63.9
Defined benefit pension plans:
Net (loss) gain arising during the year	(0.4)	0.2	0.4
Unrealized gain (losses) on securities:
Gain (losses) arising during the year	14.2	(13.5)	28.0
Reclassification adjustment for losses (gains) included in net income	1.2	0.5	(13.4)
Income tax provision (benefit) related to other comprehensive income	15.0	(12.8)	15.0
Other comprehensive income (loss), net of tax	80.9	(77.9)	48.9
Comprehensive income (loss)	$ 72.5	$ (14.3)	$ 99.2