Taxation (Details) - Reconciliation of effective tax rate (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Expected tax provision at weighted average rate	$ 53,358	$ (66,493)	$ 80,225
Permanent differences:
Non taxable investment income (loss)	(16,717)	(14,246)	(10,176)
Non taxable income (loss)	(25,711)	(3,265)	3,838
Prior year adjustments	(622)	(9,206)	16,594
Prior year adjustments on completion of IRS examinations	(19,192)	0	0
State, local and foreign taxes	18,312	42,581	44,122
Valuation allowance	(16,644)	24,990	1,346
Allocated investment income	41,727	21,483	12,386
Stock options	4,749	5,840	3,323
Non-deductible expenses	16,145	12,901	11,079
Realized capital loss carry-forward valuation allowance reduction	(24,473)	0	0
Non-deductible goodwill impairment	0	57,069	0
Non-taxable reserve release	3,096	(11,947)	0
Total Tax Expense	$ 34,028	$ 59,707	$ 162,737