CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net income	$ 101,442	$ 59,347
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	40,270	36,744
Share-based compensation expense	35,688	29,482
Operating lease right-of-use assets expense	2,843	2,551
Deferred income tax benefit	(3,729)	(7,440)
Changes in operating assets and liabilities, exclusive of effects of    acquired companies:
Accounts receivable	(30,332)	(69,058)
Income tax receivable	(21,453)	4,806
Prepaid expenses and other current assets	(9,870)	(9,987)
Accounts payable	(6,338)	550
Operating lease liabilities	(3,375)	(2,866)
Accrued liabilities	(19,136)	846
Deferred revenue	10,510	3,479
Net cash provided by operating activities	96,520	48,454
Cash flows from investing activities:
Additions to property and equipment	(16,268)	(24,052)
Purchase of marketable security investments	(79,747)	(10,117)
Proceeds from marketable security investments	40,020	39,688
Purchase of investment in common shares	(10,000)	0
Proceeds from the sale of investment in preferred shares	15,000	0
Investment in software	(2,695)	(2,232)
Cost of acquisitions, net of cash acquired	(261)	(199,220)
(Increase) decrease in other	(328)	432
Net cash used by investing activities	(54,279)	(195,501)
Cash flows from financing activities:
Increase in net borrowings on revolving line of credit	0	15,000
Purchase of treasury shares	(15,482)	(17,786)
Payment of contingent consideration	(5,619)	0
Proceeds from exercise of stock options	92,337	22,132
Contributions from employee stock purchase plan	5,177	4,609
Net cash provided by financing activities	76,413	23,955
Net increase (decrease) in cash and cash equivalents	118,654	(123,092)
Cash and cash equivalents at beginning of period	232,682	134,279
Cash and cash equivalents at end of period	$ 351,336	$ 11,187