Consolidated Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Cash flows from operating activities:
Net income	$ 109,242	$ 113,981
Adjustments to reconcile net income to net cash provided by operating activities (See Note 1)	(10,270)	(54,082)
Net cash provided by operating activities	98,972	59,899
Cash flows from investing activities:
Additions to property and equipment	(20,674)	(7,317)
Additions to capitalized software	(6,458)	(9,937)
Purchases of marketable securities	(29,407)	(43,672)
Prepayments and maturities of marketable securities	37,623	45,200
Proceeds from Sale and Maturity of Marketable Securities	64	0
Other investing activities	1,500	0
Net cash used in investing activities	(17,352)	(15,726)
Cash flows from financing activities:
Payment of contingent consideration	633	0
Purchase and retirement of common stock	(130,558)	(90,777)
Proceeds from issuance of common stock	18,593	8,893
Payment of dividends	(52,452)	(50,760)
Net cash used in financing activities	(165,050)	(132,644)
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(11,146)	3,272
Net decrease in cash, cash equivalents and restricted cash	(94,576)	(85,199)
Cash, cash equivalents and restricted cash, beginning of period	844,547	758,039	$ 758,039
Cash, cash equivalents and restricted cash, end of period	749,971	672,840	$ 844,547
Non-cash operating activities:
Operating lease right-of-use assets and net lease liabilities recorded upon adoption of ASC 842	$ 0	$ 44,169