Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Differences between our effective tax rate for financial statement purposes and the Federal statutory rate
Statutory tax rate									35.00%	35.00%	35.00%
Federal tax at statutory rate									$ 194,049	$ 124,252	$ 171,439
Nontaxable municipal bond interest and dividend received deduction									(31,939)	(29,021)	(26,968)
State income taxes, net of federal tax benefit									3,619	3,050	2,397
Foreign income taxes									40,703	25,410	32,008
Foreign tax credits									(40,703)	(25,410)	(32,008)
Uncertain tax positions (net of federal tax benefit (expense) on state positions: $719 in 2012, $212 in 2011 and $(52) in 2010)									878	38	(1,532)
Other, net									(3,420)	1,444	(605)
Income tax expense	$ 41,428	$ 46,557	$ 40,826	$ 34,376	$ 34,092	$ 22,355	$ 27,427	$ 15,889	$ 163,187	$ 99,763	$ 144,731
Effective tax rate									29.40%	28.10%	29.50%