Parent Financial Statements (Details 1) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Revenues:
Investment income and other									$ 16,969	$ 22,843	$ 29,081
Total revenues									6,318,394	5,806,301	5,188,070
Expenses:
Selling, general and administrative	145,271	130,785	122,289	116,459	119,642	106,815	108,189	117,423	514,804	452,069	394,089
Depreciation and amortization									37,369	35,048	34,746
Interest									20,550	16,011	16,266
Income before income taxes	51,111	76,514	69,444	112,777	126,568	135,338	106,783	68,482	309,846	437,171	201,419
Income tax expense									114,225	163,800	52,140
Net income	32,776	48,074	44,294	70,477	79,628	84,348	67,213	42,182	195,621	273,371	149,279
Net income per share:
Basic net income per share									$ 4.10	$ 5.52	$ 2.89
Weighted average number of common shares outstanding									47,731,265	49,522,202	51,647,267
Diluted net income per share	$ 0.67	$ 0.96	$ 0.83	$ 1.37	$ 1.59	$ 1.68	$ 1.31	$ 0.82	$ 3.82	$ 5.40	$ 2.85
Weighted average number of common shares and dilutive potential common shares outstanding	49,179,891	50,253,757	53,541,368	51,534,794	49,924,608	50,197,740	51,318,044	51,226,435	51,163,108	50,608,008	52,309,268
Parent Company [Member]
Revenues:
Service fees from subsidiaries									424,989	416,447	368,379
Investment income and other									2,030	4,208	2,476
Total revenues									427,019	420,655	370,855
Expenses:
Selling, general and administrative									362,502	321,367	262,684
Depreciation and amortization									32,442	28,375	27,256
Interest									20,422	15,871	16,225
Total expenses									415,366	365,613	306,165
Income before income taxes									11,653	55,042	64,690
Income tax expense									(4,548)	(24,155)	(465)
Equity earnings in subsidiaries									188,516	242,484	85,054
Net income									$ 195,621	$ 273,371	$ 149,279
Net income per share:
Basic net income per share									$ 4.10	$ 5.52	$ 2.89
Weighted average number of common shares outstanding									47,731,265	49,522,202	51,647,267
Diluted net income per share									$ 3.82	$ 5.40	$ 2.85
Weighted average number of common shares and dilutive potential common shares outstanding									51,163,108	50,608,008	52,309,268