Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flow from operating activities:
Net income	$ 45,013	$ 29,498
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense	15,633	15,809
Accounts Receivable, Credit Loss Expense (Reversal)	(299)	(86)
Loss on disposal of property and equipment	0	(183)
Stock-based compensation	19,441	16,780
Accretion of discounts on marketable securities	(21)	(1,060)
Deferred income taxes	1,269	3,047
Changes in operating assets and liabilities:
Accounts receivable	1,797	12,555
Prepaid expenses and other assets	(6,725)	(6,896)
Accounts payable	220	(1,189)
Accrued liabilities	(972)	(85)
Deferred revenues	5,695	12,397
Other noncurrent liabilities	0	150
Net cash provided by operating activities	81,649	81,275
Cash flow from investing activities:
Purchases of marketable securities	(162,912)	(184,829)
Sales and maturities of marketable securities	164,109	193,270
Purchases of property and equipment	(11,568)	(14,138)
Business combinations	0	(1,850)
Net cash used in investing activities	(10,371)	(7,547)
Cash flow from financing activities:
Proceeds from exercise of stock options	20,430	8,991
Payments for taxes related to net share settlement of equity awards	(11,115)	(7,411)
Principal payments under finance lease obligations	(61)	(836)
Repurchase of common stock	(54,182)	(24,117)
Net cash used in financing activities	(44,928)	(23,373)
Net increase in cash, cash equivalents and restricted cash	26,350	50,355
Cash, cash equivalents and restricted cash at beginning of period	88,759	42,226
Cash, cash equivalents and restricted cash at end of period	$ 115,109	$ 92,581