Consolidated Statements of Changes in Equity (USD $)	Common Shares $1 Par Value [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income [Member]	Retained Earnings [Member]	Subtotal [Member]	Noncontrolling Interest [Member]	Total
Balance, at Dec. 31, 2009	$ 243,288,000	$ 1,529,064,000	$ 985,032,000	$ 1,604,263,000	$ 4,361,647,000	$ 12,850,000	$ 4,374,497,000
Comprehensive income (loss):
Net change in unrealized gain (loss) on investments, net of taxes			(333,239,000)		(333,239,000)		(333,239,000)
Net change in unrealized foreign exchange gain (loss), net of taxes			(13,243,000)		(13,243,000)		(13,243,000)
Net change in unrealized gain (loss) on derivative instruments, net of taxes			(1,005,000)		(1,005,000)		(1,005,000)
Net change in pension liability and postretirement benefits, net of taxes			936,000		936,000		936,000
Net income (loss)				(43,665,000)	(43,665,000)	(1,108,000)	(44,773,000)
Comprehensive income (loss)					(390,216,000)	(1,108,000)	(391,324,000)
Contributions from noncontrolling interests						753,000	753,000
Distributions to noncontrolling interests						(2,373,000)	(2,373,000)
Share-based compensation expense		2,711,000			2,711,000		2,711,000
Exercise of options to purchase common shares, including excess tax benefit	30,000	598,000			628,000		628,000
Purchase of common shares for treasury	(1,000)	(17,000)			(18,000)		(18,000)
Balance, at Jun. 30, 2010	243,317,000	1,532,356,000	638,481,000	1,560,598,000	3,974,752,000	10,122,000	3,984,874,000
Balance, at Dec. 31, 2010	243,808,000	1,542,964,000	1,687,363,000	3,482,623,000	6,956,758,000	6,623,000	6,963,381,000
Comprehensive income (loss):
Net change in unrealized gain (loss) on investments, net of taxes			(374,701,000)		(374,701,000)		(374,701,000)
Net change in unrealized foreign exchange gain (loss), net of taxes			2,086,000		2,086,000		2,086,000
Net change in pension liability and postretirement benefits, net of taxes			(5,000)		(5,000)		(5,000)
Net income (loss)				196,816,000	196,816,000	428,000	197,244,000
Comprehensive income (loss)					(175,804,000)	428,000	(175,376,000)
Contributions from noncontrolling interests						598,000	598,000
Distributions to noncontrolling interests						(4,369,000)	(4,369,000)
Change in interest in consolidated subsidiary		(1,624,000)			(1,624,000)	1,474,000	(150,000)
Share-based compensation expense		14,460,000			14,460,000		14,460,000
Exercise of warrants to purchase common shares	523,000	(523,000)
Exercise of options to purchase common shares, including excess tax benefit	246,000	6,844,000			7,090,000		7,090,000
Purchase of common shares for treasury	(4,000)	(151,000)			(155,000)		(155,000)
Balance, at Jun. 30, 2011	$ 244,573,000	$ 1,561,970,000	$ 1,314,743,000	$ 3,679,439,000	$ 6,800,725,000	$ 4,754,000	$ 6,805,479,000