Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fixed income securities-available for sale
Fixed maturity securities - available for sale	$ 6,185,456	$ 6,281,781
Equity securities - available for sale, at fair value (cost: 2013 - $319,499 and 2012 - $275,827)	350,352	284,639
Held-to-maturity Securities, Fair Value	0	0
Short-term investments*	267,434	363,053
Other Investments	2,810	20,925
Restricted cash and securities	2,041	2,043
Premium, claims and other receivables	72,398	68,207
Other assets	459	349
Total assets measured at fair value	6,880,950	7,020,997
Notes payable	676,400	636,363
Accounts payable and accrued liabilities - earnout liability	9,112	9,052
Accounts payable and accrued liabilities - forward contract	1,411	3,194
Total liabilities measured at fair value	686,923	648,609
Fair Value, Inputs, Level 1 [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	105,667	174,520
Equity securities - available for sale, at fair value (cost: 2013 - $319,499 and 2012 - $275,827)	350,352	284,639
Short-term investments*	193,033	251,988
Other Investments Held At Fair Value	2,810	20,925
Total assets measured at fair value	651,862	732,072
Fair Value, Inputs, Level 2 [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	6,070,174	6,107,097
Short-term investments*	74,401	111,065
Restricted cash and securities	2,041	2,043
Premium, claims and other receivables	72,398	68,207
Total assets measured at fair value	6,219,014	6,288,412
Notes payable	676,400	636,363
Accounts payable and accrued liabilities - earnout liability	2,041	2,043
Accounts payable and accrued liabilities - forward contract	1,411	3,194
Total liabilities measured at fair value	679,852	641,600
Fair Value, Inputs, Level 3 [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	9,615	164
Other assets	459	349
Total assets measured at fair value	10,074	513
Accounts payable and accrued liabilities - earnout liability	7,071	7,009
Total liabilities measured at fair value	7,071	7,009
US Government Agencies Debt Securities [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	126,249	199,607
US Government Agencies Debt Securities [Member] \| Fair Value, Inputs, Level 1 [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	105,667	174,520
US Government Agencies Debt Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	20,582	25,087
US States and Political Subdivisions Debt Securities [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	1,043,001	1,065,811
US States and Political Subdivisions Debt Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	1,043,001	1,065,811
Special Purpose Revenue Bonds Of States Municipalities And Political Subdivisions [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	2,251,190	2,200,331
Special Purpose Revenue Bonds Of States Municipalities And Political Subdivisions [Member] \| Fair Value, Inputs, Level 2 [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	2,241,742	2,200,331
Special Purpose Revenue Bonds Of States Municipalities And Political Subdivisions [Member] \| Fair Value, Inputs, Level 3 [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	9,448
Corporate Debt Securities [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	1,301,625	1,315,170
Corporate Debt Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	1,301,458	1,315,006
Corporate Debt Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	167	164
Residential Mortgage Backed Securities [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	655,623	664,887
Residential Mortgage Backed Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	655,623	664,887
Commercial Mortgage Backed Securities [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	522,063	524,289
Commercial Mortgage Backed Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	522,063	524,289
Asset-backed Securities [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	42,530	33,275
Asset-backed Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	42,530	33,275
Foreign Government Debt Securities [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	243,175	278,411
Foreign Government Debt Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Fixed income securities-available for sale
Fixed maturity securities - available for sale	$ 243,175	$ 278,411

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