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	$ 146,527	$ 147,462	$ 169,571
Adjustments to reconcile net income to cash provided by operations:
Depreciation and amortization	76,672	61,759	53,395
Share-based compensation expense	59,967	52,740	37,348
Provision for losses and sales adjustments - accounts receivable	1,636	(569)	2,031
Operating lease right-of-use assets - non cash	5,397
Deferred income tax benefit	(6,088)	(5,069)	(33,664)
Changes in operating assets and liabilities, exclusive of effects of acquired companies:
Accounts receivable	(65,738)	(50,916)	(33,091)
Income tax receivable	(1,925)	6,642	(8,444)
Prepaid expenses and other current assets	(8,976)	(588)	(6,958)
Accounts payable	7,403	(2,416)	878
Operating lease liabilities	(6,113)
Accrued liabilities	1,516	(2,445)	6,050
Deferred revenue	44,442	43,603	8,639
Net cash provided by operating activities	254,720	250,203	195,755
Cash flows from investing activities:
Additions to property and equipment	(37,236)	(27,424)	(43,057)
Purchase of marketable security investments	(54,742)	(115,625)	(59,779)
Proceeds from marketable security investments	70,796	81,205	28,786
Capitalized software development costs	(4,804)	0	0
Cost of acquisitions, net of cash acquired	(218,734)	(178,093)	(11,344)
(Increase) decrease in other	(295)	1,682	(1)
Net cash used by investing activities	(245,015)	(238,255)	(85,395)
Cash flows from financing activities:
Decrease in net borrowings on revolving line of credit	0	0	(10,000)
Purchase of treasury shares	(17,786)	(146,553)	(7,474)
Proceeds from exercise of stock options	96,908	74,907	49,845
Contributions from employee stock purchase plan	9,576	8,051	7,044
Net cash provided (used) by financing activities	88,698	(63,595)	39,415
Net increase (decrease) in cash and cash equivalents	98,403	(51,647)	149,775
Cash and cash equivalents at beginning of period	134,279	185,926	36,151
Cash and cash equivalents at end of period	$ 232,682	$ 134,279	$ 185,926