Schedule I - Condensed Financial Information of Registrant (Condensed Cash Flow Statement) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Financial Statements, Captions [Line Items]
Net Cash Flows Provided by Operating Activities	$ 95,839	$ 32,540	$ 103,380
CASH FLOWS FROM INVESTING ACTIVITIES:
Sales of investments	696,534	1,350,003	1,760,336
Maturities of investments	93,225	135,394	189,137
Purchases of investments	(722,223)	(1,678,582)	(1,814,431)
Purchases of property and equipment	(59,525)	(73,101)	(64,260)
Sales (purchases) of restricted investments and other	(7,432)	5,466	(10,656)
Net cash provided by (used in) investing activities	579	(12,558)	222,227
CASH FLOWS FROM FINANCING ACTIVITIES:
Net (decrease) increase in checks outstanding, net of deposits	(23,842)	23,842	(46,718)
Excess tax benefit on share-based compensation	620	6,089	1,349
Proceeds from exercise of stock options and employee stock purchases	10,762	16,941	13,356
Borrowings under financing arrangements	345,000	110,000	978,500
Repayments of borrowings under financing arrangements	(345,000)	(122,500)	(872,212)
Repurchase of common stock	(77,810)	(69,496)	(389,850)
Net cash (used in) provided by financing activities	(3,373)	89,875	(445,492)
Net (decrease) increase in cash and cash equivalents	93,045	109,857	(119,885)
Cash and cash equivalents, beginning of year	340,110	230,253	350,138
Cash and cash equivalents, end of year	433,155	340,110	230,253
SUPPLEMENTAL CASH FLOWS DISCLOSURE:
Interest paid	30,789	31,134	31,332
Income taxes paid	80,119	5,001	55,882
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net Cash Flows Provided by Operating Activities	111,385	165,141	252,100
CASH FLOWS FROM INVESTING ACTIVITIES:
Sales of investments	6,060	0	0
Maturities of investments	877	0	0
Purchases of investments	(6,841)	0	0
Purchases of property and equipment	(53,632)	(68,116)	(48,046)
Increase (decrease) in notes receivable from Subsidiaries	0	7,000	(24,000)
Capital contributions returned to Parent	2,300	1,500	1,796
Capital contributions to subsidiaries	(7,500)	(17,560)	(400)
Sales (purchases) of restricted investments and other	161	876	(13,361)
Net cash provided by (used in) investing activities	(58,575)	(76,300)	(84,011)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net (decrease) increase in checks outstanding, net of deposits	5	(44)	(37)
Excess tax benefit on share-based compensation	287	3,222	544
Net borrowings from subsidiaries	39,487	(9,103)	(14,246)
Proceeds from exercise of stock options and employee stock purchases	10,762	16,941	13,356
Borrowings under financing arrangements	345,000	110,000	978,500
Repayments of borrowings under financing arrangements	(345,000)	(122,500)	(872,212)
Repurchase of common stock	(77,810)	(69,496)	(389,850)
Net cash (used in) provided by financing activities	(27,269)	(70,980)	(283,945)
Net (decrease) increase in cash and cash equivalents	25,541	17,861	(115,856)
Cash and cash equivalents, beginning of year	105,809	87,948	203,804
Cash and cash equivalents, end of year	131,350	105,809	87,948
SUPPLEMENTAL CASH FLOWS DISCLOSURE:
Interest paid	30,789	31,134	31,332
Income taxes paid	$ 80,119	$ 5,001	$ 55,882