Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities:
Net income	$ 120.0	$ 66.6
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Amortization and depreciation	13.8	13.8
Share-based payments expense	8.8	11.0
Deferred income tax benefit, net	3.2	(6.9)
Net realized investment (gains) loss	(64.5)	5.2
Undistributed earnings from alternative investment portfolio	(11.4)	(13.9)
Loss on disposals of fixed assets, net	0.1	0.0
Change in:
Accrued investment income	0.5	(1.2)
Receivables	(161.9)	(53.3)
Deferred acquisition costs	3.5	(1.5)
Ceded unearned premiums	(136.2)	(87.4)
Reserves for losses and loss adjustment expenses	83.2	(71.1)
Unearned premiums	103.0	67.0
Ceded reinsurance payable and funds held	80.3	80.2
Income taxes	4.4	14.9
Accrued underwriting expenses and other liabilities	12.8	156.6
Other, net	(64.5)	(54.1)
Cash (used in) provided by operating activities	(4.9)	125.9
Cash flows from investing activities:
Sales of fixed maturity investments	751.6	882.0
Maturities and mandatory calls of fixed maturity investments	168.8	288.7
Sales of equity securities	32.2	104.9
Sales of other investments	31.1	38.1
Purchases of fixed maturity investments	(888.5)	(1,237.5)
Purchases of equity securities	(32.4)	(113.3)
Purchases of other investments	(38.2)	(23.3)
Change in foreign regulatory deposits and voluntary pools	6.3	13.1
Change in short-term investments	67.7	(80.7)
Settlements of foreign currency exchange forward contracts	9.9	2.3
Cash acquired with acquisition of Ariscom		15.6
Purchases of fixed assets	(15.7)	(11.0)
Other, net	(22.5)	(16.7)
Cash provided by (used in) investing activities	70.3	(137.8)
Cash flows from financing activities:
Activity under stock incentive plans	0.9	0.2
Repurchase of Company's common shares	0.0	(19.4)
Payment of cash dividends to common shareholders	(22.7)	(18.7)
Cash used in financing activities	(21.8)	(37.9)
Effect of exchange rate changes on cash	(0.5)	(0.1)
Change in cash	43.1	(49.9)
Cash, beginning of year	139.2	176.6
Cash, end of period	182.3	126.7
Ariscom [Member]
Cash flows from investing activities:
Cash acquired with acquisition of Ariscom	$ 0.0	$ 15.6