CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net income	$ 451,295	$ 419,375	$ 259,251
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	60,516	59,255	67,678
Operating lease right-of-use assets amortization	18,459
Deferred income tax benefit	(14,511)	(33,675)	(2,693)
Provision for bad debts	2,928	1,577	1,474
Stock-based compensation expense	116,190	83,346	53,154
Other	2,778	410	21
Changes in operating assets and liabilities:
Accounts receivable	(154,403)	(74,455)	(14,406)
Other receivables and current assets	(26,182)	(30,241)	(18,498)
Other long-term assets	(5,622)	1,839	(435)
Accounts payable, accrued expenses and current liabilities	38,543	19,920	27,045
Accrued income taxes	575	1,086	1,215
Deferred revenue	17,245	56,213	20,648
Other long-term liabilities	(7,875)	(19,662)	33,206
Net cash provided by operating activities	499,936	484,988	427,660
Cash flows from investing activities:
Acquisitions, net of cash acquired	(787,196)	(283,026)	(63,885)
Capital expenditures	(44,940)	(21,762)	(19,149)
Other investing activities	(1,412)	(7,443)	(11,631)
Net cash used in investing activities	(833,548)	(312,231)	(94,665)
Cash flows from financing activities:
Proceeds from long-term debt	500,000	0	0
Purchase of treasury stock	(59,116)	(269,801)	(336,042)
Restricted stock withholding taxes paid in lieu of issued shares	(42,431)	(28,879)	(11,112)
Proceeds from shares issued for stock-based compensation	34,093	41,019	52,503
Other financing activities	(3,137)	(5,014)	0
Net cash provided by (used in) financing activities	429,409	(262,675)	(294,651)
Effect of exchange rate fluctuations on cash and cash equivalents	(842)	(14,444)	20,678
Net increase (decrease) in cash and cash equivalents	94,955	(104,362)	59,022
Cash and cash equivalents, beginning of period	777,139	881,501	822,479
Cash and cash equivalents, end of period	872,094	777,139	881,501
Supplemental disclosures of cash flow information:
Income taxes paid	86,770	87,244	116,389
Interest paid	787	114	199
Fair value of common stock issued as consideration in connection with acquisitions	$ 307,173	$ 0	$ 0