Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net income	$ 48,672	$ 42,904
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense	23,486	21,224
Provision for Doubtful Accounts	156	0
Loss on disposal of property and equipment	196	31
Stock-based compensation	25,163	22,672
Amortization of premiums and (accretion) of discounts on marketable securities	(1,402)	(586)
Deferred income taxes	7,296	(4,024)
Changes in operating assets and liabilities:
Accounts receivable	14,355	5,800
Prepaid expenses and other assets	(6,485)	(5,733)
Accounts payable	(1,336)	182
Accrued liabilities	1,275	5,803
Deferred revenues	15,413	12,351
Other non-current liabilities	160	(1,804)
Net cash provided by operating activities	126,949	98,820
Cash flows from investing activities:
Purchases of marketable securities	(259,286)	(242,056)
Sales and maturities of marketable securities	263,874	218,865
Purchases of property and equipment	(19,473)	(19,496)
Business combinations	(1,850)	(3,359)
Payments to Acquire Investments	(625)	(2,500)
Net cash used in investing activities	(17,360)	(48,546)
Cash flows from financing activities:
Proceeds from exercise of stock options	11,014	20,896
Payments for taxes related to net share settlement of equity awards	(10,864)	(12,010)
Principal payments under finance lease obligations	(1,273)	(1,203)
Repurchase of common stock	(73,877)	(46,542)
Net cash used in financing activities	(75,000)	(38,859)
Effect of Exchange Rate on Cash and Cash Equivalents, Continuing Operations	0	(42)
Net increase in cash, cash equivalents and restricted cash	34,589	11,373
Cash, cash equivalents and restricted cash at beginning of period	42,226	87,791
Cash, cash equivalents and restricted cash at end of period	$ 76,815	$ 99,164