Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flow from operating activities:
Net income	$ 49,139	$ 67,756
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense	26,752	23,975
Bad debt expense	247	392
Loss on disposal of property and equipment	12	9
Stock-based compensation	56,218	29,930
Amortization of premiums on marketable securities	2,985	163
Deferred income taxes	(15,962)	5,061
Changes in operating assets and liabilities:
Accounts receivable	15,665	13,351
Prepaid expenses and other assets	(5,460)	(6,071)
Accounts payable	200	326
Accrued liabilities	9,912	72
Deferred revenues	21,033	6,333
Net cash provided by operating activities	160,741	141,297
Cash flow from investing activities:
Purchases of marketable securities	(255,051)	(290,534)
Sales and maturities of marketable securities	295,336	263,296
Purchases of property and equipment	(20,089)	(22,742)
Proceeds from disposal of property and equipment	6	0
Purchases of intangible assets	(1,080)	(1,500)
Net cash provided by (used in) investing activities	19,122	(51,480)
Cash flow from financing activities:
Repurchases of common stock	(94,919)	(91,881)
Proceeds from exercise of stock options	10,948	23,962
Payments for taxes related to net share settlement of equity awards	(24,194)	(16,338)
Principal payments under finance lease obligations	(90)	(92)
Net cash used in financing activities	(108,255)	(84,349)
Net increase in cash, cash equivalents and restricted cash	71,608	5,468
Cash, cash equivalents and restricted cash at beginning of period	75,332	88,759
Cash, cash equivalents and restricted cash at end of period	$ 146,940	$ 94,227