Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flow from operating activities:
Net income	$ 67,756	$ 48,672
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense	23,975	23,486
Bad debt expense	392	156
Loss on disposal of property and equipment	9	196
Stock-based compensation	29,930	25,163
Amortization of premiums (accretion of discounts) on marketable securities	163	(1,402)
Deferred income taxes	5,061	7,296
Changes in operating assets and liabilities:
Accounts receivable	13,351	14,355
Prepaid expenses and other assets	(6,071)	(6,568)
Accounts payable	326	(1,336)
Accrued liabilities	72	1,518
Deferred revenues	6,333	15,413
Net cash provided by operating activities	141,297	126,949
Cash flow from investing activities:
Purchases of marketable securities	(290,534)	(259,286)
Sales and maturities of marketable securities	263,296	263,874
Purchases of property and equipment	(22,742)	(19,473)
Acquisition of businesses, net of cash acquired, and purchases of intangible assets	(1,500)	(1,850)
Purchase of privately-held investment	0	(625)
Net cash used in investing activities	(51,480)	(17,360)
Cash flow from financing activities:
Repurchases of common stock	(91,881)	(73,877)
Proceeds from exercise of stock options	23,962	11,014
Payments for taxes related to net share settlement of equity awards	(16,338)	(10,864)
Principal payments under finance lease obligations	(92)	(1,273)
Net cash used in financing activities	(84,349)	(75,000)
Net increase in cash, cash equivalents and restricted cash	5,468	34,589
Cash, cash equivalents and restricted cash at beginning of period	88,759	42,226
Cash, cash equivalents and restricted cash at end of period	$ 94,227	$ 76,815