Schedule I - Condensed Financial Information of Registrant (Condensed Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Current Assets:
Cash and cash equivalents	$ 996,854	$ 869,133	$ 433,155	$ 340,110
Available for sale securities	2,218,367	1,791,060
Other assets	338,890	220,122
Deferred taxes	91,005	57,911
Assets held for sale	0	50,000
Total current assets	5,324,043	4,515,617
Property and equipment, net	146,053	84,328
Goodwill	558,886	558,886	565,900
Other intangible assets, net	9,060	11,822
Deferred taxes	12,230	33,081
Other assets	319,794	187,630
Total Assets	6,397,646	5,395,934
Current Liabilities:
Line of Credit, Current	285,000	0
Other current liabilities	85,132	71,988
Total current liabilities	3,871,910	2,944,503
Other noncurrent liabilities	292,947	242,705
Total Liabilities	$ 4,564,566	$ 3,686,712
Commitments and contingencies
Stockholders’ Equity:
Common stock	$ 154	$ 153
Additional paid-in capital	1,497,562	1,444,705
Treasury common stock, at cost	(2,454,939)	(2,341,652)
Retained earnings	2,794,954	2,609,277
Accumulated other comprehensive income	(4,651)	(3,261)	(32,900)	27,000
Total Stockholders’ Equity	1,833,080	1,709,222	1,628,811	1,557,030
Total Liabilities and Stockholders’ Equity	6,397,646	5,395,934
Parent Company [Member]
Current Assets:
Cash and cash equivalents	28,063	61,212	$ 131,350	$ 105,809
Other assets	64,064	36,740
Deferred taxes	365	11,538
Assets held for sale	0	50,000
Due from subsidiaries	79,629	128,967
Total current assets	172,121	288,457
Property and equipment, net	118,483	53,016
Goodwill	312,732	312,732
Other intangible assets, net	0	573
Investment in subsidiaries	3,359,203	3,060,191
Deferred taxes	3,667	36,453
Other assets	69,481	70,760
Total Assets	4,035,687	3,822,182
Current Liabilities:
Due to subsidiaries	155,502	284,654
Deferred taxes	19,619	34,684
Line of Credit, Current	285,000	0
Other current liabilities	121,767	130,580
Total current liabilities	581,888	449,918
Intercompany Notes Payable, long term	1,069,224	1,047,947
Long term debt	399,709	499,504
Other noncurrent liabilities	151,786	115,591
Total Liabilities	$ 2,202,607	$ 2,112,960
Commitments and contingencies
Stockholders’ Equity:
Common stock	$ 154	$ 153
Additional paid-in capital	1,497,562	1,444,705
Treasury common stock, at cost	(2,454,939)	(2,341,652)
Retained earnings	2,794,954	2,609,277
Accumulated other comprehensive income	(4,651)	(3,261)
Total Stockholders’ Equity	1,833,080	1,709,222
Total Liabilities and Stockholders’ Equity	$ 4,035,687	$ 3,822,182