CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities:
Net income	$ 59,347	$ 76,986
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	36,744	29,649
Share-based compensation expense	29,482	23,490
Deferred income tax benefit	(7,440)	(5,196)
Changes in operating assets and liabilities, exclusive of effects of acquired companies:
Accounts receivable	(69,058)	(48,870)
Income taxes	4,806	(1,762)
Prepaid expenses and other current assets	(9,472)	(815)
Accounts payable	550	(4,599)
Accrued liabilities	16	(12,185)
Deferred revenue	3,479	10,532
Net cash provided by operating activities	48,454	67,230
Cash flows from investing activities:
Additions to property and equipment	(24,052)	(14,952)
Purchase of marketable security investments	(10,117)	(74,850)
Proceeds from marketable security investments	39,688	39,154
Investment in software	(2,232)	0
Cost of acquisitions, net of cash acquired	(199,220)	(157,152)
Decrease (increase) in other	432	(186)
Net cash used by investing activities	(195,501)	(207,986)
Cash flows from financing activities:
Increase in net borrowings on revolving line of credit	15,000	0
Purchase of treasury shares	(17,786)	0
Proceeds from exercise of stock options	22,132	44,317
Contributions from employee stock purchase plan	4,609	3,760
Net cash provided by financing activities	23,955	48,077
Net decrease in cash and cash equivalents	(123,092)	(92,679)
Cash and cash equivalents at beginning of period	134,279	185,926
Cash and cash equivalents at end of period	$ 11,187	$ 93,247