Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net income	$ 69,336	$ 57,304	$ 40,440
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense	31,201	28,904	20,636
Bad debt expense	247	86	657
Loss on disposal of property and equipment	202	9	161
Stock-based compensation	34,892	30,090	26,961
Amortization of premiums and accretion of discounts on investments	(1,597)	(1,136)	1,324
Deferred income taxes	7,095	(2,521)	(2,718)
Changes in operating assets and liabilities:
Accounts receivable	(2,456)	(11,467)	(17,966)
Prepaid expenses and other assets	(6,012)	(4,970)	(53)
Accounts payable	(1,076)	3,515	(454)
Accrued liabilities	715	1,426	1,485
Increase (Decrease) in Contract with Customer, Liability	28,060	24,725	29,830
Other noncurrent liabilities	0	(501)	7,343
Net cash provided by operating activities	160,607	125,464	107,646
Payments to Acquire Marketable Securities	331,131	339,862	299,891
Cash flows from investing activities:
Proceeds from Sale and Maturity of Marketable Securities	328,350	285,224
Sales and maturities of investments			231,996
Purchases of property and equipment	(27,573)	(22,775)	(37,818)
Payments to Acquire Businesses, Gross	(4,050)	(13,633)	(12,482)
Payments to Acquire Investments	625
Capitalized software development costs			0
Net cash used in investing activities	(35,029)	(93,546)	(118,195)
Payments for Repurchase of Common Stock	(86,424)	(85,040)	0
Cash flows from financing activities:
Proceeds from exercise of stock options	24,831	24,053	31,327
Payments Related to Tax Withholding for Share-based Compensation	(15,743)	(14,879)	(20,924)
Repayments of Long-term Capital Lease Obligations	(1,709)	(1,617)	0
Net cash provided by financing activities	(79,045)	(77,483)	10,403
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	46,533	(45,565)	(146)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	42,226	87,791	87,937
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	88,759	42,226	87,791
Supplemental disclosures of cash flow information
Interest Paid, Excluding Capitalized Interest, Operating Activities	107	168	3
Cash paid for income taxes, net of refunds	3,031	2,693	1,584
Non-cash investing and financing activities
Business acquisitions recorded in Intangible Assets and Accrued liabilities	1,650	4,676	1,000
Purchases of property and equipment recorded in accounts payable and accrued liabilities	$ 235	4,190	$ 2,765
privately-held companies [Member] | Preferred Stock
Cash flows from investing activities:
Payments to Acquire Investments		$ 2,500