Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$ 185,677	$ 145,629	$ 170,126
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization and depreciation	22,533	29,786	38,589
Asset impairment charges	1,884	88,536	0
Share-based compensation expense	29,451	28,334	29,930
Deferred income taxes	(10,894)	(16,564)	8,645
Excess tax benefit on share-based compensation	(4,855)	(2,230)	(620)
Net realized gain on investments	(191)	(2,710)	(24,061)
Other changes	38,119	29,838	31,539
Changes in assets and liabilities, net of effects of acquisitions and dispositions:
Premiums receivable and unearned premiums	46,315	(549,786)	(83,822)
Other current assets, receivables and noncurrent assets	(315,238)	(444,288)	1,425
Amounts receivable/payable under government contracts	(98,039)	39,754	20,896
Reserves for claims and other settlements	(402,643)	911,960	(53,898)
Accounts payable and other liabilities	938,976	517,742	(42,910)
Net cash provided by operating activities	431,095	776,001	95,839
CASH FLOWS FROM INVESTING ACTIVITIES:
Sales of investments	953,092	441,430	696,534
Maturities of investments	104,095	98,901	93,225
Purchases of investments	(1,538,128)	(665,200)	(722,223)
Purchases of property and equipment	(60,949)	(62,010)	(59,525)
Sales (purchases) of restricted investments and other	(4,759)	2,027	(7,432)
Net cash (used in) provided by investing activities	(546,649)	(184,852)	579
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from exercise of stock options and employee stock purchases	18,972	27,727	10,762
Excess tax benefit on share-based compensation	4,855	2,230	620
Repurchases of common stock	(112,977)	(152,549)	(77,810)
Borrowings under financing arrangements	360,000	0	345,000
Repayment of borrowings under financing arrangements	(175,000)	0	(345,000)
Net decrease in checks outstanding, net of deposits	0	0	(23,842)
Customer funds administered	147,425	(32,579)	86,897
Net cash provided by (used in) financing activities	243,275	(155,171)	(3,373)
Net increase in cash and cash equivalents	127,721	435,978	93,045
Cash and cash equivalents, beginning of year	869,133	433,155	340,110
Cash and cash equivalents, end of year	996,854	869,133	433,155
SUPPLEMENTAL CASH FLOWS DISCLOSURE:
Interest paid	31,622	29,670	30,789
Income taxes paid	$ 276,468	$ 83,499	$ 80,119