CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net income	$ 99,737	$ 115,910
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	56,547	45,627
Share-based compensation expense	44,369	37,966
Operating lease right-of-use assets - non cash	3,979
Deferred income tax benefit	(10,329)	(5,034)
Changes in operating assets and liabilities, exclusive of effects of acquired companies:
Accounts receivable	(35,544)	(31,393)
Income taxes	4,553	(1,942)
Prepaid expenses and other current assets	(7,630)	983
Accounts payable	1,548	(4,729)
Operating lease liabilities	(4,530)
Accrued liabilities	(1,379)	1,523
Deferred revenue	27,206	20,442
Net cash provided by operating activities	178,527	179,353
Cash flows from investing activities:
Additions to property and equipment	(28,833)	(23,460)
Purchase of marketable security investments	(27,322)	(92,638)
Proceeds from marketable security investments	56,854	60,208
Investment in software	(3,540)	0
Cost of acquisitions, net of cash acquired	(199,870)	(167,308)
(Increase) decrease in other	(493)	857
Net cash used by investing activities	(203,204)	(222,341)
Cash flows from financing activities:
Purchase of treasury shares	(17,786)	0
Proceeds from exercise of stock options	62,295	70,536
Contributions from employee stock purchase plan	7,327	5,978
Net cash provided by financing activities	51,836	76,514
Net increase in cash and cash equivalents	27,159	33,526
Cash and cash equivalents at beginning of period	134,279	185,926
Cash and cash equivalents at end of period	$ 161,438	$ 219,452