Condensed Statements of Operations and Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income
Loss on sale of investments									$ (188)	$ (299)	$ 0
Expenses
Compensation and employee benefits									118,571	104,221	95,373
Other operating expenses									41,648	38,856	36,087
Total expenses	55,698	54,238	52,673	50,070	53,034	50,368	48,481	43,434	212,679	195,317	193,421
Income tax benefit	(8,846)	(9,800)	(8,350)	(8,913)	(8,630)	(8,315)	(5,927)	(7,145)	(35,909)	(30,017)	(19,077)
Net Income	28,054	29,294	28,677	26,730	26,546	25,628	22,702	20,768	112,755	95,644	75,516
Total Comprehensive Income									120,854	57,327	89,991
Parent Company
Income
Dividends from subsidiaries									78,500	65,445	78,209
Loss on sale of investments									0	(3,248)	0
Other income									199	966	566
Intercompany charges for services									9,283	7,387	16,041
Total income									87,982	70,550	94,816
Expenses
Compensation and employee benefits									10,773	9,175	12,392
Other operating expenses									6,824	6,536	10,267
Total expenses									17,597	15,711	22,659
Income before income tax benefit and equity in undistributed net income of subsidiaries									70,385	54,839	72,157
Income tax benefit									2,919	3,676	2,319
Income before equity in undistributed net income of subsidiaries									73,304	58,515	74,476
Equity in undistributed net income of subsidiaries									39,451	37,129	1,040
Net Income									112,755	95,644	75,516
Total Comprehensive Income									$ 120,854	$ 57,327	$ 89,991