Consolidated Statements Of Cash Flows (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Cash flows from operating activities:
Net income (loss)	$ 57.0	$ (83.3)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Amortization and depreciation	27.9	21.8
Share-based payments expense	7.9	2.5
Excess tax expense from share-based payment arrangements	0	0.1
Deferred income tax provision, net	2.6	10.3
Net realized investment gains	(18.6)	(37.7)
Loss on disposals of fixed assets, net	0.3	0.2
Change in:
Accrued investment income	3.5	2.0
Receivables	34.6	54.6
Deferred acquisition costs	(6.2)	2.3
Ceded unearned premiums	(33.9)	(63.7)
Reserves for losses and loss adjustment expenses	(74.6)	197.4
Unearned premiums	129.4	69.3
Ceded reinsurance payable and funds held	(63.4)	(93.8)
Income taxes	(10.1)	(10.4)
Accrued underwriting expenses	13.2	3.9
Other, net	(6.1)	(19.3)
Cash provided by operating activities	63.5	56.2
Cash flows from investing activities:
Sales of fixed maturity investments	886.9	1,021.0
Maturities and mandatory calls of fixed maturity investments	364.9	296.7
Sales of equity securities	9.1	29.8
Sales of other investments	2.5	2.4
Purchases of fixed maturity investments	(1,147.3)	(1,199.1)
Purchases of equity securities	(91.4)	(75.5)
Purchases of other investments	(12.7)	(51.9)
Change in foreign regulatory deposits	(20.2)	(13.2)
Change in short-term investments	(78.8)	21.0
Settlements of foreign currency exchange forward contracts	(0.6)	9.0
Purchases of fixed assets, net	(26.9)	(10.8)
Acquisition of subsidiaries	(1.4)	(0.5)
Other, net	2.7	1.2
Cash (used) provided by investing activities	(113.2)	30.1
Cash flows from financing activities:
Proceeds from issuance of senior unsecured fixed rate notes, net	139.2	0
Activity under stock incentive plans	0.7	0.9
Repurchase of Company's common shares	(38.6)	(35.9)
Excess tax expense from share-based payment arrangements	0	(0.1)
Payment of cash dividend to common shareholders	(9.3)	(10.0)
Cash provided (used) by financing activities	92.0	(45.1)
Effect of exchange rate changes on cash	(0.5)	(4.9)
Change in cash	41.8	36.3
Cash, beginning of period	100.9	83.5
Cash, end of period	$ 142.7	$ 119.8