Qualys (QLYS) 10-K 27 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Jan. 31, 2019	Jun. 30, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	QUALYS, INC.
Entity Central Index Key	1,107,843
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Amendment Flag	false
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		39,038,263
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 2,395

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 41,026	$ 86,591
Marketable Securities, Current	248,140	201,823
Accounts receivable, net of allowance of $702 and $769 at December 31, 2016 and 2015, respectively	75,825	64,412
Prepaid expenses and other current assets	13,974	16,524
Total current assets	378,965	369,350
Marketable Securities, Noncurrent	76,710	67,224
Long-term investments	2,500	0
Property and equipment, net	61,442	58,557
Deferred tax assets, net	26,387	25,066
Intangible assets, net	21,976	12,401
Goodwill	7,225	1,549
Restricted cash	1,200	1,200
Other noncurrent assets	9,275	2,178
Total assets	585,680	537,525
Current liabilities:
Accounts payable	5,588	1,144
Accrued liabilities	25,130	21,444
Deferred revenues, current	164,624	143,186
Capital Lease Obligations, Current	1,565	0
Total current liabilities	196,907	165,774
Deferred revenues, noncurrent	20,423	17,136
Other noncurrent liabilities	10,361	11,071
Total liabilities	227,691	193,981
Commitments and contingencies (Note 6)
Stockholders’ equity:
Preferred stock: $0.001 par value; 20,000,000 shares authorized, no shares issued and outstanding at December 31, 2016 and 2015	0	0
Common stock, $0.001 par value; 1,000,000,000 shares authorized, 35,841,001 and 34,414,631 shares issued and outstanding at December 31, 2016 and 2015, respectively	39	39
Additional paid-in capital	330,572	304,155
Accumulated other comprehensive loss	(586)	(574)
Accumulated deficit	27,964	39,924
Total stockholders’ equity	357,989	343,544
Total liabilities and stockholders’ equity	$ 585,680	$ 537,525

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Allowance for Doubtful Accounts Receivable	$ 683	$ 816
Preferred Stock, Par Value (in dollars per share)	$ 0.001	$ 0.001
Preferred Stock, Shares Authorized	20,000,000	20,000,000
Preferred Stock, Shares Issued	0	0
Preferred Stock, Shares Outstanding	0	0
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.001	$ 0.001
Common Stock, Shares Authorized	1,000,000,000	1,000,000,000
Common Stock, Shares, Issued	39,015,034	38,598,117
Common Stock, Shares, Outstanding	39,015,034	38,598,117

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Revenues	$ 278,889	$ 230,828	$ 197,925
Cost of revenues	66,185	51,580	43,128
Gross profit	212,704	179,248	154,797
Operating expenses:
Research and development	53,255	42,816	36,591
Sales and marketing	70,039	63,855	58,985
General and administrative	39,049	35,334	29,114
Total operating expenses	162,343	142,005	124,690
Income from operations	50,361	37,243	30,107
Other income (expense), net:
Interest expense	(172)	(3)	(26)
Interest income	6,080	2,674	1,320
Other expense, net	(801)	(536)	(972)
Total other income (expense), net	5,107	2,135	322
Income before income taxes	55,468	39,378	30,429
Provision for (benefit from) income taxes	(1,836)	(1,062)	11,205
Net income	$ 57,304	$ 40,440	$ 19,224
Net income per share:
Basic (usd per share)	$ 1.47	$ 1.08	$ 0.55
Diluted (usd per share)	$ 1.37	$ 1.01	$ 0.50
Weighted average shares used in computing net income per share:
Basic (in shares)	38,876	37,443	35,247
Diluted (in shares)	41,897	40,071	38,369

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 57,304	$ 40,440	$ 19,224
Change in net unrealized loss on investments, net of tax	(261)	(462)	(57)
Reclassification adjustment for net change realized and included in net income, net of tax	289	44	112
Total change in unrealized gain (loss) on marketable securities, net of tax	28	(418)	55
Change in net unrealized loss, net of tax	(40)	0	0
Other comprehensive (loss) income, net of tax	(12)	(418)	55
Comprehensive income	$ 57,292	$ 40,022	$ 19,279

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income	$ 14,400	$ 2,857	$ 57,304	$ 40,440	$ 57,304	$ 40,440	$ 19,224	$ 19,224
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense					28,904	20,636	16,994
Bad debt expense					86	657	199
Loss on disposal of property and equipment					9	161	55
Stock-based compensation					30,090	26,961	20,149
Amortization of premiums and accretion of discounts on investments					(1,136)	1,324	1,000
Excess tax benefits from stock-based compensation					0	0	(8,700)
Deferred income taxes					(2,521)	(2,718)	(440)
Changes in operating assets and liabilities:
Accounts receivable					(11,467)	(17,966)	(4,898)
Prepaid expenses and other assets					(4,970)	(53)	(2,107)
Accounts payable					3,515	(454)	(1,220)
Accrued liabilities					1,426	1,485	9,696
Deferred revenues					24,725	29,830	17,903
Other noncurrent liabilities					(501)	7,343	1,455
Net cash provided by operating activities					125,464	107,646	69,310
Cash flows from investing activities:
Purchases of investments					(339,862)	(299,891)	(222,953)
Sales and maturities of investments					285,224	231,996	149,708
Purchases of property and equipment					(22,775)	(37,818)	(23,245)
Payments to Acquire Businesses, Gross			(12,500)		(13,633)	(12,482)	0
Payments to Acquire Investments					2,500	0
Capitalized software development costs							0
Net cash used in investing activities					(93,546)	(118,195)	(96,490)
Payments for Repurchase of Common Stock					(85,040)	0	0
Cash flows from financing activities:
Proceeds from exercise of stock options					24,053	31,327	15,157
Payments Related to Tax Withholding for Share-based Compensation					(14,879)	(20,924)	(438)
Excess tax benefits from stock-based compensation					0	0	8,700
Repayments of Long-term Capital Lease Obligations					(1,617)	0	0
Net cash provided by financing activities					(77,483)	10,403	23,419
Cash and cash equivalents at beginning of period			86,591		86,591
Cash and cash equivalents at end of period	41,026	86,591			41,026	86,591
Supplemental disclosures of cash flow information
Cash paid for interest expense			168	27		3
Cash paid for income taxes, net of refunds			2,693	856		1,584
Non-cash investing and financing activities
Business acquisitions recorded in Intangible Assets and Accrued liabilities			4,676	0		1,000
Purchases of property and equipment recorded in accounts payable and accrued liabilities			$ 4,190	$ 1,438		2,765
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect					(45,565)	(146)	(3,761)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 42,226	$ 87,791			$ 42,226	$ 87,791	$ 87,937	$ 91,698

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balance at Dec. 31, 2015	$ 195,566	$ 34	$ 223,228	$ (211)	$ (27,485)
Balance (in shares) at Dec. 31, 2015		34,414,631
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	19,224				19,224
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	55			55
Change in unrealized loss on investments	55
Issuance of common stock upon exercise of stock options	$ 15,157	$ 2	15,155
Issuance of common stock upon exercise of stock options (shares)	1,399,157	1,399,157
Issuance of common stock upon vesting of restricted stock units (in shares)		25,213
Excess tax benefits from stock-based compensation	$ 8,700		8,700
Issuance of common stock in exchange for services	26		26
Issuance of common stock in exchange for services (shares)		2,000
Taxes from release of the restricted share units	(438)		(438)
Stock-based compensation	20,123		20,123
Balance at Dec. 31, 2016	258,413	$ 36	266,794	(156)	(8,261)
Balance (in shares) at Dec. 31, 2016		35,841,001
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	40,440
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(418)
Change in unrealized loss on investments	(418)
Issuance of common stock upon exercise of stock options	$ 31,327	$ 3	31,324
Issuance of common stock upon exercise of stock options (shares)	2,997,095	2,997,095
Issuance of common stock upon vesting of restricted stock units (in shares)		217,111
Taxes from release of the restricted share units	$ (20,924)		(20,924)
Taxes related to net share settlement of equity awards, shares		(457,090)
Stock-based compensation	26,961		26,961
Balance at Dec. 31, 2017	343,544	$ 39	304,155	(574)	39,924
Balance (in shares) at Dec. 31, 2017		38,598,117
Accumulated deficit	39,924
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	57,304				57,304
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(12)			(12)
Change in unrealized loss on investments	28
Issuance of common stock upon exercise of stock options	$ 24,053	$ 1	24,052
Issuance of common stock upon exercise of stock options (shares)	1,183,235	1,183,235
Stock Repurchased During Period, Shares		(1,088,899)
Treasury Stock, Value, Acquired, Cost Method	$ (85,040)	$ (1)	(13,064)		(71,975)
Issuance of common stock upon vesting of restricted stock units (in shares)		524,903
Taxes from release of the restricted share units	(14,879)		(14,879)
Stock-based compensation	30,308		30,308
Balance at Dec. 31, 2018	357,989	$ 39	$ 330,572	$ (586)	$ 27,964
Balance (in shares) at Dec. 31, 2018		39,015,034
Accumulated deficit	$ 27,964

The Company and Summary of Sign

The Company and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
The Company and Summary of Significant Accounting Policies	NOTE 1. The Company and Summary of Significant Accounting Policies Description of Business Qualys, Inc. (the “Company”, "we", "us", "our") was incorporated in the state of Delaware on December 30, 1999. The Company is headquartered in Foster City, California and has wholly-owned subsidiaries throughout the world. The Company is a pioneer and leading provider of cloud-based security and compliance solutions that enable organizations to identify security risks to their IT infrastructures, help protect their IT systems and applications from ever-evolving cyber-attacks and achieve compliance with internal policies and external regulations. The Company’s cloud solutions address the growing security and compliance complexities and risks that are amplified by the dissolving boundaries between internal and external IT infrastructures and web environments, the rapid adoption of cloud computing and the proliferation of geographically dispersed IT assets. Organizations can use the Company’s integrated suite of solutions delivered on its Qualys Cloud Platform to cost-effectively obtain a unified view of their security and compliance posture across globally-distributed IT infrastructures. Basis of Presentation The accompanying consolidated financial statements and footnotes have been prepared by the Company in accordance with accounting principles generally accepted in the United States (“U.S. GAAP”) as well as the instructions to Form 10-K and the rules and regulations of the U.S. Securities and Exchange Commission ("SEC"). In the opinion of management, the accompanying consolidated financial statements reflect all adjustments, which include only normal recurring adjustments, necessary for the fair presentation of the Company’s consolidated financial position, results of operations and cash flows for the periods presented. The accompanying consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All significant intercompany transactions and balances have been eliminated upon consolidation. Use of Estimates The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make certain estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of assets and liabilities at the date of the consolidated financial statements and the reported results of operations during the reporting period. The Company’s management regularly assesses these estimates, which primarily affect revenue recognition, the valuation of accounts receivable, goodwill and intangible assets, capitalization of internally developed software, stock-based compensation and the provision for income taxes. Actual results could differ from those estimates and such differences may be material to the accompanying consolidated financial statements. Concentration of Credit Risk The Company invests its cash and cash equivalents with major financial institutions. Cash balances with any one institution at times may be in excess of federally insured limits. Cash equivalents are invested in high-quality investment grade financial instruments and are diversified. The Company has not experienced any losses in such accounts and believes it is not exposed to any significant credit risk. Credit risk with respect to accounts receivable is dispersed due to the large number of customers. Collateral is not required for accounts receivable. As of December 31, 2018 and 2017 , no customer or channel partner accounted for more than 10% of the Company's revenues and accounts receivable balance. Cash, Cash Equivalents, Short-Term and Long-Term Investments Cash and cash equivalents include cash held in banks, highly liquid money market funds, commercial paper, and fixed-income U.S. government agency securities, all with original maturities of three months or less when acquired. The Company’s investments consist of fixed-income U.S. government agency securities, corporate bonds, asset-backed securities and commercial paper. Management determines the appropriate classification of the Company's investments at the time of purchase and reevaluates such designation at each balance sheet date. The Company classifies its investments as either short-term or long-term based on each instrument's underlying contractual maturity date. Cash equivalents are stated at cost, which approximates fair market value. Short-term and long-term investments are classified as available-for-sale and are carried at fair value. Unrealized gains and losses in fair value are reported in other comprehensive income (loss). When the available-for-sale securities are sold, cost is based on the specific identification method, and the realized gains and losses are included in other income (expense) in the consolidated statements of operations. Short-term and long-term investments are reviewed quarterly for impairment that is deemed to be other-than-temporary. An investment is considered other-than-temporarily impaired when its fair value is below its amortized cost and (1) there is an intent to sell the security, (2) it is “more likely than not” that the security will be sold before recovery of its amortized cost basis or (3) the present value of expected cash flows from the investment is not expected to recover the entire amortized cost basis. Declines in value that are considered to be other-than-temporary and adjustments to amortized cost for the amortization of premiums and the accretion of discounts are recorded in other income (expense). Interest and dividends are recorded in interest income as earned. Accounts Receivable Accounts receivable are recorded at the invoiced amount and do not bear interest. The allowance for doubtful accounts represents the Company’s best estimate of the amount of probable credit losses and is determined based on a review of existing accounts receivable by aging category to identify significant customers or invoices with collectability issues. For those invoices not specifically reviewed, the reserve is calculated based on the age of the receivable and historical write-offs. Any change in the assumptions used in analyzing a specific account receivable may result in an additional provision for doubtful accounts being recognized in the period in which the change occurs. When the Company ultimately concludes that a receivable is uncollectible, the balance is written off against the allowance for doubtful accounts. Payments subsequently received on such receivables are credited back to the allowance for doubtful accounts. Cost Method Investments In the second quarter of fiscal 2018, the Company invested $2.5 million in a privately-held company. The Company used the cost method of accounting to account for the investment because it does not hold a controlling interest in this entity and the Company does not have the ability to exercise significant influence over the entity's operating and financial policies. The investment is included in long term assets on the accompanying consolidated balance sheets. The Company's cost method investment is assessed for impairment when events or changes in circumstances indicate that the carrying amount may not be recoverable. The Company has not recorded any dividends or other-than-temporary impairment charges related to its cost method investment. The fair value of the investment is not readily available, and there are no quoted market prices for the investment. Property and Equipment, net Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation is computed using the straight-line method over the estimated useful lives of the assets, which range from three to five years. Leasehold improvements are amortized on a straight-line basis over the lesser of the estimated useful life of the asset or the lease term. The Company purchases physical scanner appliances and other computer equipment that are provided to customers on a subscription basis. This equipment is recorded within property and equipment on the accompanying consolidated balance sheet, and the depreciation is recorded to cost of revenues over an estimated useful life of three years. Upon retirement or disposal, the cost of assets and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is reflected in the consolidated statements of operations. Repairs and maintenance that do not extend the life of an asset are expensed as incurred and major improvements are capitalized as property and equipment. Leases On certain of our operating lease agreements, the Company may receive rent free periods or escalating rent payments over the terms of the leases. The Company recognizes rent expense under these agreements on a straight-line basis over the term of the lease, starting when the Company takes possession of the property from the landlord. The Company records the difference between the recognized rent expense and the amounts payable under the lease as a short-term or long-term deferred rent liability. When the Company receives tenant allowances upon entering into certain leases, the Company records the allowances as an offset to short-term or long-term deferred rent liability and amortizes them using the straight-line method as a reduction to rent expense over the term of the lease. Impairment of Long-Lived Assets The Company evaluates its long-lived assets, which consist of property and equipment, and intangible assets subject to amortization, for indicators of possible impairment when events or changes in circumstances indicate the carrying amount of an asset may not be recoverable. Impairment exists if the carrying amounts of such assets exceed the estimates of future undiscounted cash flows expected to be generated by such assets. Should an impairment exist, the impairment loss would be measured based on the excess carrying value of the asset over the asset’s estimated fair value. In each of 2018, 2017 and 2016, the Company had no impairment of long-lived assets. Goodwill and Intangible Assets Goodwill represents the excess of the purchase price over the fair value of the net tangible and identifiable intangible assets acquired in a business combination and is not subject to amortization. Goodwill and other intangible assets with indefinite lives are not amortized, but tested for impairment annually or if certain circumstances indicate a possible impairment may exist. These tests are performed at the reporting unit level. The Company’s operations are organized as one reporting unit. In testing for a potential impairment of goodwill, the Company first performs a qualitative assessment of its reporting unit to determine if it is more likely than not (a more than 50% likelihood) that the fair value of the reporting unit is less than its carrying amount. If the fair value is not considered to be less than the carrying amount, no further evaluation is necessary. The Company performed the annual qualitative assessment for the year ended December 31, 2018 and concluded there was no potential impairment of goodwill. In testing for a potential impairment of intangible assets with indefinite lives that are not subject to amortization, the Company first performs a qualitative assessment to determine if it is more likely than not (a more than 50% likelihood) that the fair value of the indefinite-lived intangible assets is less than the carrying amount. If the fair value is not considered to be less than the carrying amount, no further evaluation is necessary. The Company performs the annual qualitative assessment in the fourth quarter each fiscal year. There were no such impairment losses during 2018, 2017 or 2016. If the qualitative assessment indicates there is more than a 50% likelihood that the fair value is less than the carrying amount of the reporting unit or the intangible asset, the Company would perform a two-step test. In the first step, the carrying value of the reporting unit or intangible asset is compared to its estimated fair value. If the estimated fair value is less than the carrying value, then potential impairment exists. In the second step, for goodwill, the Company calculates the amount of any impairment by determining the implied fair value of goodwill using a hypothetical purchase price allocation, similar to that which would be applied if it were an acquisition and the purchase price was equivalent to fair value as calculated in the first step. Impairment is equivalent to any excess of goodwill carrying value over its implied fair value. For indefinite-lived intangible assets, the Company performs the currently prescribed quantitative impairment test by comparing the fair value of the indefinite-lived intangible asset with its carrying value. Certain other intangible assets acquired are amortized over their estimated useful lives and tested for impairment if certain circumstances indicate an impairment may exist. The Company’s intangible assets are comprised primarily of existing technology, patent license, and non-competition agreements and are amortized over periods ranging from three to fourteen years on a straight-line basis. As of December 31, 2018 , the Company has not written down any of these intangible assets as a result of impairment. Internally Developed Software Costs incurred in the development phase are capitalized and amortized over the product’s estimated useful life, which is three years. Capitalized costs include salaries, benefits, and stock-based compensation charges for employees that are directly involved in developing its cloud security platform during the post planning and implementation phases. Capitalized costs related to internally developed software under development are treated as construction in progress until the program, feature or functionality is ready for its intended use, at which time amortization commences. These capitalized costs are included in other noncurrent assets on the accompanying consolidated balance sheets. For 2018, 2017 and 2016, the Company capitalized $1.3 million (of which $0.2 million was stock-based compensation), $0.4 million , and zero of costs related to internally developed software, respectively. As of December 31, 2018 and 2017, unamortized internally developed software costs totaled $1.2 million and $0.3 million , respectively. Amortization of internally developed software is reflected in cost of revenues. Costs associated with minor enhancements and maintenance are expensed as incurred. Management evaluates the useful lives of these assets on an annual basis and tests for impairment whenever events or changes in circumstances occur that could impact the recoverability of these assets. Business Combinations We apply the provisions of ASC 805, Business Combinations, in accounting for our acquisitions. It requires us to recognize separately from goodwill the assets acquired and the liabilities assumed at their acquisition date fair values. Goodwill as of the acquisition date is measured as the excess of consideration transferred over the net of the acquisition date fair values of the assets acquired and the liabilities assumed. While we use our best estimates and assumptions to accurately value assets acquired and liabilities assumed at the acquisition date as well as any contingent consideration, where applicable, our estimates are inherently uncertain and subject to refinement. As a result, during the measurement period, which may be up to one year from the acquisition date, we record adjustments to the assets acquired and liabilities assumed with the corresponding offset to goodwill. Upon the conclusion of the measurement period or final determination of the values of assets acquired or liabilities assumed, whichever comes first, any subsequent adjustments are recorded to our consolidated statements of operations. Derivative Financial Instruments Derivative financial instruments are utilized by the Company to reduce foreign currency exchange risks. The Company uses foreign currency forward contracts to mitigate the impact of foreign currency fluctuations of certain non-U.S. dollar denominated asset positions, to date primarily cash and accounts receivable (non-designated), as well as to manage foreign currency fluctuation risk related to forecasted transactions (designated). The Company accounts for these instruments as either non-designated or cash flow hedges, respectively. Open contracts are recorded within prepaid expenses and other current assets or accrued liabilities in the consolidated balance sheets. Gains and losses resulting from currency exchange rate movements on non-designated forward contracts are recognized in other income (expense). Any gains or losses from derivatives designated as cash flow hedges are first accumulated in other comprehensive income (AOCI) and then reclassified to revenue when the hedged item impacts the consolidated financial statements. During the year ended December 31, 2018, the Company began a hedging strategy to reduce its exposure to foreign currency exchange rate fluctuations for forecasted subscription renewals and new orders in both GBP and Euro. We use sell-forward currency contracts accounted for as cash flow hedges against a designated portion of forecasted subscription renewals and new orders . Upon executing a hedging contract and quarterly thereafter, the Company assesses hedge effectiveness using regression analysis. The Company includes time value in its effectiveness testing and the entire change in the value of hedge contracts was recorded as unrealized gains or losses in accumulated other comprehensive income (AOCI) within stockholders’ equity on the Company's consolidated balance sheet as of December 31, 2018. The unrealized gains or losses in AOCI will be reclassified into revenue when the respective hedged transactions affect earnings. As of December 31, 2018, the amount of unrealized gains and losses related to the hedged forecasted transactions reported in AOCI that is expected to be reclassified into revenue within the next 12 months was not material. The cash flow effects of the Company's derivative contracts for the year ended December 31, 2018 were included within net cash provided by operating activities on its consolidated statements of cash flows. The Company had notional amounts on foreign currency exchange contracts designated as cash flow hedges outstanding of €12.9 million and £4.1 million as of December 31, 2018. The unrealized FX losses on these contracts were recorded in AOCI and are insignificant. At December 31, 2018 , the Company had two outstanding non-designated forward contracts with notional amounts of €16.0 million and £6.3 million , respectively, both with the expiry date of January 31, 2019 . At December 31, 2017 , the Company had two non-designated outstanding forward contracts with notional amounts of €7.0 million and £4.8 million , which expired on January 31, 2018 . These forward contracts had insignificant fair value at both December 31, 2018 and 2017 . These derivatives were not designated as hedges. These instruments were valued using Level 2 inputs. The following summarizes the gains (losses) recognized from non-designated forward contracts and other foreign currency transactions: Year Ended December 31, 2018 2017 2016 Net gains (losses) from forward contracts $ 543 $ (1,665 ) $ 554 Other foreign currency transaction (losses) gains (1,120 ) 1,310 (1,324 ) Total foreign exchange loss, net $ (577 ) $ (355 ) $ (770 ) Stock-Based Compensation The Company recognizes the fair value of its employee stock options and restricted stock units (RSUs) over the requisite service period for those awards ultimately expected to vest. The fair value of each option is estimated on date of grant using the Black-Scholes-Merton option pricing model and the fair value of each restricted stock unit is based on the fair value of the Company's stock on the date of grant. Forfeitures are estimated on the date of grant and revised if actual or expected forfeiture activity differs materially from original estimates. Option grants to non-employees are accounted for at the fair value of the equity instrument issued, as calculated using the Black-Scholes-Merton option-pricing model and the expense is recognized over the vesting periods of the options. The value of options granted to non-employees is re-measured as they vest over a performance period. Revenue Recognition The Company derives revenues from subscriptions that require customers to pay a fee in order to access the Company’s cloud solutions. Customers generally enter into one year renewable subscriptions though some customers do enter into subscriptions with longer terms. The subscription fee entitles the customer to an unlimited number of scans for a specified number of networked devices or web applications and, if requested by a customer as part of their subscription, a specified number of physical or virtual scanner appliances. Revenue is recognized when control of these subscription services is transferred to our customers, in an amount that reflects the consideration we expect to be entitled to in exchange for those services. The Company’s physical and virtual scanner appliances are requested by certain customers as part of their subscriptions in order to scan IT infrastructures within their firewalls and do not function without, and are not sold separately from, subscriptions for the Company’s solutions. In some limited cases, the Company also provides certain computer equipment used to extend its Qualys Cloud Platform into its customers’ private cloud environment. Customers are required to return physical scanner appliances and computer equipment if they do not renew their subscriptions.Physical equipment (scanners and private cloud platforms) are accounted for as operating leases and revenue is recognized over the subscription term. We determine revenue recognition through the following steps: • Identification of the contract, or contracts, with a customer; • Identification of the performance obligations in the contract; • Determination of the transaction price; • Allocation of the transaction price to the performance obligations in the contract; and • Recognition of revenue when, or as, we satisfy a performance obligation. At the inception of a customer contract, we make an assessment as to that customer's ability to pay for the services provided. We assess collectability based on a number of factors, including credit worthiness of the customer along with past transaction history. In addition, we perform periodic evaluations of our customers’ financial condition. The Company recognizes revenues for certain limited scan arrangements, for which expiration dates can be extended, on an as-used basis. Deferred revenues consist of customer contracts billed or cash received that will be recognized in the future under subscriptions existing at the balance sheet date. The current portion of deferred revenues represents amounts that are expected to be recognized within one year of the balance sheet date. Costs of shipping and handling charges incurred by the Company associated with physical scanner appliances and other computer equipment are included in cost of revenues. Sales taxes and other taxes collected from customers to be remitted to government authorities are excluded from revenues. Advertising Expenses Advertising costs are expensed as incurred and include costs of advertising and promotional materials. The Company incurred advertising costs of $87 thousand , $482 thousand and $124 thousand for 2018 , 2017 and 2016 , respectively. Income Taxes The Company provides for the effect of income taxes in its consolidated financial statements using the asset and liability method which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the consolidated financial statements. Under this method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases, net operating loss carryovers, and tax credit carry forwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in the period that includes the enactment date. Income tax expense or benefit is recognized for the amount of taxes payable or refundable for the current liabilities for the tax consequences of events that have been recognized in an entity’s financial statements or significant assumptions, judgments and estimates to determine its current provision (benefit) for income taxes, its deferred tax assets and liabilities, and any valuation allowance to be recorded against its deferred tax assets. The Company's judgments, assumptions and estimates relating to the current provision (benefit) for income taxes include the geographic mix and amount of income (loss), its possible outcomes of current and future audits conducted by foreign and domestic tax authorities. The anticipating the tax positions the Company will record in the consolidated financial statements before actually preparing and filing the tax returns. The Company's estimates and assumptions may differ from the actual results as reflected in its income tax required adjustments when they are identified or resolved. Changes in the Company's business, tax laws or laws, and developments in current and future tax audits, could significantly impact the amounts provided for income taxes in the Company's results of operations, financial position, or cash flows. Deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to tax benefit carry-forwards and to differences between the financial statement amounts of assets and liabilities and their respective tax basis. The Company regularly reviews its deferred tax assets for recoverability and establishes a valuation allowance if it is more likely than not that assets will not be realized. To make this assessment, the Company takes into account predictions of the amount and category of taxable income from various sources and all available positive and negative evidence about these possible sources of taxable potential effect of negative and positive evidence is commensurate with the extent to which the strength of the evidence can be objectively verified. The Company applies a two-step approach to determining the financial statement recognition and measurement of uncertain tax positions. The Company only recognizes an income tax expense or benefit with respect to uncertain tax positions in its financial statements that the Company judges is more likely than not to be sustained solely on its technical merits in a tax audit, including resolution of any related appeals or litigation processes. To make this judgment, the Company must interpret complex and sometimes ambiguous tax laws, regulations and administrative practices. If an income tax position meets the more likely than not recognition threshold, then the Company must measure the amount of the tax benefit to be recognized by determining the largest amount of tax benefit that has a greater than a 50% likelihood of being realized upon effective settlement with a taxing authority that has full knowledge of all of the relevant facts. It is inherently difficult and subjective to estimate such amounts, as this requires the Company to determine the probability of various possible settlement outcomes. To determine if a tax position is effectively settled after a tax examination has been completed, the Company must also estimate the likelihood that another taxing authority could review the respective tax position. The Company must also determine when it is reasonably possible that the amount of unrecognized tax benefits will significantly increase or decrease in the 12 months after each fiscal year-end. These judgments are difficult because a taxing authority may change its behavior as a result of the Company's disclosures in its financial statements. The Company must reevaluate its income tax positions on a quarterly basis to consider factors such as changes in facts or circumstances, changes in tax law, effectively settled issues under audit, and new audit activity. Such a change in recognition or measurement would result in recognition of a tax benefit or an additional charge to the tax provision. The Company's policy is to recognize interest and penalties related to unrecognized tax benefits as a component of the provision for income taxes. Comprehensive Income (Loss) Other comprehensive income (loss) consists of unrealized gains (losses) on available-for-sale investments, net of tax, and derivative financial instruments including our hedging instruments designated as cash flow hedges which are not included in the Company’s net income. Total comprehensive income includes net income and other comprehensive income (loss) and is included in the consolidated statements of comprehensive income. Foreign Currency Transactions The Company’s operations are conducted in various countries around the world and the financial statements of its foreign subsidiaries are reported in the U.S. dollar as their respective functional currency. Monetary assets and liabilities denominated in foreign currencies have been re-measured into U.S. dollars using the exchange rates in effect at the balance sheet date, and income and expenses are re-measured at average exchange rates during the period. Foreign currency re-measurement gains and losses and foreign currency transaction gains and losses are recognized in other income (expense), net. The Company recorded total foreign currency transaction losses of $0.6 million , $0.4 million and $0.8 million during 2018 , 2017 and 2016 , respectively. Fair Value Measurements Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. For certain of the Company’s financial instruments, including certain cash equivalents, accounts receivable, accounts payable, and other current liabilities, the carrying amounts approximate their fair value due to the relatively short maturity of these balances. The Company measures and reports certain cash equivalents, investments and derivative foreign currency forward contracts at fair value in accordance with the provisions of the authoritative accounting guidance that addresses fair value measurements. This guidance establishes a hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the most observable inputs be used when available. The hierarchy is broken down into three levels based on the reliability of inputs as follows: Level 1 —Valuations based on quoted prices in active markets for identical assets or liabilities. Level 2 —Valuations based on other than quoted prices in active markets for identical assets and liabilities, quoted prices for identical or similar assets or liabilities in inactive markets, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3— Valuations based on inputs that are generally unobservable and typically reflect management’s estimates of assumptions that market participants would use in pricing the asset or liability. The Company's financial instruments consist of assets measured using Level 1 and 2 inputs. Level 1 assets include a highly liquid money market fund, which is valued using unadjusted quoted prices that are available in an active market for an identical asset. Level 2 assets include fixed-income U.S. government agency securities, commercial paper, corporate bonds, asset-backed securities and derivative financial instruments consisting of foreign currency forward contracts. The securities, bonds and commercial paper are valued using prices from independent pricing services based on quoted prices in active markets for similar instruments or on industry models using data inputs such as interest rates and prices that can be directly observed or corroborated in active markets. The foreign currency forward contracts are valued using observable inputs , including currency spot

Fair Value of Financial Instrum

Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	NOTE 2. Fair Value of Financial Instruments The Company's cash and cash equivalents, short-term investments, and long-term investments consist of the following: December 31, 2018 Amortized Cost Unrealized Gains Unrealized Losses Fair Value (in thousands) Cash and cash equivalents: Cash $ 40,913 $ — $ — $ 40,913 Money market funds 113 — — 113 Total 41,026 — — 41,026 Short-term marketable securities : Commercial paper 3,237 — — 3,237 Corporate bonds 30,906 — (84 ) 30,822 Asset-backed securities 10,447 — (15 ) 10,432 U.S. government agencies 203,734 9 (94 ) 203,649 Total 248,324 9 (193 ) 248,140 Long-term marketable securities : Asset-backed securities 22,945 10 (28 ) 22,927 U.S. government agencies 18,804 — (53 ) 18,751 Corporate bonds 35,322 3 (293 ) 35,032 Total 77,071 13 (374 ) 76,710 Total $ 366,421 $ 22 $ (567 ) $ 365,876 December 31, 2017 Amortized Cost Unrealized Gains Unrealized Losses Fair Value (in thousands) Cash and cash equivalents: Cash $ 86,500 $ — $ — $ 86,500 Money market funds 91 — — 91 Total 86,591 — — 86,591 Short-term investments: Commercial paper 12,623 — (3 ) 12,620 Corporate bonds 38,425 1 (64 ) 38,362 U.S. government agencies 151,058 — (217 ) 150,841 Total 202,106 1 (284 ) 201,823 Long-term investments: Asset-backed securities 4,998 — (12 ) 4,986 U.S. government agencies 24,269 — (54 ) 24,215 Corporate bonds 38,198 — (175 ) 38,023 Total 67,465 — (241 ) 67,224 Total $ 356,162 $ 1 $ (525 ) $ 355,638 The following table sets forth by level within the fair value hierarchy the fair value of the Company's available-for-sale securities measured on a recurring basis, excluding cash and money market funds: December 31, 2018 Level 1 Level 2 Level 3 Fair Value (in thousands) Commercial paper $ — $ 3,237 $ — $ 3,237 U.S. government agencies — 222,400 — 222,400 Corporate bonds — 65,854 — 65,854 Asset-backed securities — 33,359 — 33,359 Total $ — $ 324,850 $ — $ 324,850 December 31, 2017 Level 1 Level 2 Level 3 Fair Value (in thousands) Commercial paper $ — $ 12,620 $ — $ 12,620 U.S. government agencies — 175,056 — 175,056 Corporate bonds — 76,385 — 76,385 Asset-backed securities — 4,986 — 4,986 Total $ — $ 269,047 $ — $ 269,047 There were no transfers between Level 1, Level 2 or Level 3 of the fair value hierarchy, as determined at the end of each reporting period. The following summarizes the fair value of securities classified as available-for-sale by contractual maturity: December 31, 2018 Mature within One Year After One Year through Two Years Over Two Years Fair Value (in thousands) Commercial paper $ 3,237 $ — $ — $ 3,237 U.S. government agencies 203,649 18,751 — 222,400 Corporate bonds 30,822 33,531 1,501 65,854 Asset-backed securities 29,026 4,333 — 33,359 Total $ 266,734 $ 56,615 $ 1,501 $ 324,850

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Property and Equipment, net	NOTE 3. Property and Equipment, Net Property and equipment consist of the following: December 31, 2018 2017 (in thousands) Computer equipment $ 93,530 $ 77,883 Computer software 26,030 20,447 Scanner appliances 15,356 14,325 Furniture, fixtures and equipment 5,814 5,075 Equipment under capital lease 3,503 — Leasehold improvements 16,439 16,067 Total property and equipment 160,672 133,797 Less: accumulated depreciation and amortization (99,230 ) (75,240 ) Property and equipment, net $ 61,442 $ 58,557 Physical scanner appliances and other computer equipment that are or will be subject to leases by customers have a net carrying value of $7.9 million and $6.8 million at December 31, 2018 and 2017, respectively, including assets that have not been placed in service of $1.8 million and $0.9 million , respectively. Other fixed assets not placed in service at December 31, 2018 and 2017 were $3.7 million and $9.6 million , respectively. Depreciation and amortization expense relating to property and equipment was $25.1 million , $19.9 million and 16.6 million for 2018 , 2017 and 2016 , respectively. On November 20, 2017, the Company moved its headquarters office from Redwood City, California to Foster City, California. Due to the move, the Company incurred a loss of disposal of $0.2 million from abandoning the Redwood City office facilities. The gross amount of abandoned costs was $2.4 million with accumulated depreciation of $2.2 million and a net book value of $0.2 million . The loss was recognized in operating expenses.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	Revenue from Contracts with Customers On January 1, 2018, the Company adopted ASC 606 using the modified retrospective method applied to those contracts which were not completed as of that date. Results for reporting periods beginning after January 1, 2018 are presented under ASC 606, while prior period amounts are not adjusted and continue to be reported under the accounting standards in effect for the prior period. The Company implemented internal controls to enable the preparation of financial information on adoption. The impact of the standard on the Company's financial statements relates to the Company's accounting for sales commissions. The Company previously expensed sales commissions as incurred. Under ASC 606, the Company is required to capitalize certain contract acquisition costs consisting primarily of commissions paid related to new business and upsells. Applying the practical expedient in ASC 340-40-25-4, the Company expenses commissions related to its contract renewals. As a result of the adoption, the Company recorded an increase to retained earnings of $2.7 million as of January 1, 2018, which was the net cumulative impact associated with the capitalization of sales commissions. Additionally, the Company recorded a corresponding commission asset balance of $3.5 million and a related deferred tax liability of $0.8 million as of January 1, 2018. There was no impact to the Company's revenues as a result of adopting ASC 606. Incremental direct costs of obtaining a contract, which consist of sales commissions primarily for new business and upsells, are deferred and amortized over the estimated life of the customer relationship if renewals are expected and the renewal commission is not commensurate with the initial commission. The Company amortizes the capitalized commission cost as a selling expense on a straight-line basis over a period of five years. The Company classifies deferred commissions as current or noncurrent based on the timing of when it expects to recognize the expense. The current and noncurrent portions of deferred commissions are included in prepaid expenses and other current assets and other noncurrent assets, respectively, in its consolidated balance sheets. Applying the practical expedient in ASC 340-40-25-4, the Company expenses commissions related to its contract renewals that have a contract term of one year or less. Capitalized costs to obtain contracts, current and noncurrent are as follows (in thousands): December 31, 2018 January 1, 2018 Commission asset, current $ 1,480 $ 704 Commission asset, noncurrent $ 4,692 $ 2,819 For the year ended December 31, 2018 , the Company recognized $1.2 million of commission expense from amortization of its commission assets. During the same period, there was no impairment loss related to the capitalized costs. Contract liabilities (deferred revenue) balances are as follows (in thousands): December 31, 2018 ASC 606 Operating Leases Total Deferred revenue, current $ 152,204 $ 12,420 $ 164,624 Deferred revenue, noncurrent 18,286 2,137 20,423 Total $ 170,490 $ 14,557 $ 185,047 January 1, 2018 ASC 606 Operating Leases Total Deferred revenue, current $ 130,579 $ 12,607 $ 143,186 Deferred revenue, noncurrent 15,419 1,717 17,136 Total $ 145,998 $ 14,324 $ 160,322 The Company records deferred revenue when cash payments are received or due in advance of its performance. The increase in the Company's deferred revenue balances is primarily driven by cash payments received or due in advance of satisfying the Company's performance obligations, offset by revenue recognized in the period. The Company recognized $141.3 million and $112.7 million of subscription revenue during the year ended December 31, 2018 and December 31, 2017, respectively, for amount that were included in the deferred revenue balance as of December 31, 2017 and December 31, 2016 , respectively. The Company's performance obligation is typically satisfied ratably over the subscription term as its cloud-based offerings are delivered to customers electronically and over time. In addition, the Company recognizes revenues for certain limited scan arrangements on an as-used basis. The Company recognizes revenue related to the professional services based on time and materials or completion of milestones stated in the contracts. As the vast majority of the company’s offerings are subscription based, the company rarely needs to allocate the transaction price to all separate performance obligations. For contracts that include scanners and PCPs, the company recognizes revenue in proportion to the standalone selling prices ("SSP") of the underlying services at contract inception. If a SSP is not directly observable, the Company determines the SSP using information that may include market conditions and other observable inputs. The Company typically has more than one SSP for individual products and services due to the stratification of those products and services by customers and circumstances. In these instances, the Company may use information such as the size of the customer and volume purchased in determining the SSP. The Company's transaction prices typically do not include variable consideration and are a fixed amount for a specific period of time, and the majority of contracts are twelve months with certain customers signing longer term deals. In general, the Company does not offer rights of return, performance bonuses, customer loyalty programs, payments via non-cash methods, refunds, volume rebates, incentive payments, penalties, price concessions or payments or discounts contingent on future events. Consideration is fixed at the time of the contract, and governed by the price list to which that particular customer is subject. The Company’s customer and partner-specific pricing is negotiated and agreed upon via individual customer contracts. In some of its contracts, the Company incorporates tiered pricing based on the number of IP addresses the customer can scan. As customers are required to purchase larger quantities to qualify for the lower-priced tiers, the Company does not grant its customers any material rights. When customers increase their purchased quantities, the Company accounts for the additional purchased quantities and related price change prospectively as the pricing does not impact subscription services previously provided. Physical equipment (scanners and private cloud platforms) are accounted for as operating leases and revenue is recognized over the subscription term. Accounts receivable, net, consists of the following (in thousands): December 31, 2018 January 1, 2018 ASC 606 receivables $ 71,387 $ 60,984 Operating lease receivables 5,121 4,244 Less: allowance for doubtful accounts (683 ) (816 ) Total accounts receivable, net $ 75,825 $ 64,412 The Company's payment terms vary by the type and location of its customer and the products or services offered. The term between invoicing and when payment is due is not significant. For certain products or services and customer types, the Company requires payment before the products or services are delivered to the customer. The following table sets forth the expected revenue from all remaining performance obligations as of December 31, 2018 (in thousands): ASC 606 Expected Revenue Operating Lease Expected Revenue Total Expected Revenue 2019 $ 46,682 $ 5,067 $ 51,749 2020 24,608 2,194 26,802 2021 10,730 1,071 11,801 2022 1,111 39 1,150 2023 348 9 357 2024 and thereafter 20 — 20 Total $ 83,499 $ 8,380 $ 91,879 Revenues allocated to remaining performance obligations represents contracted revenues that have not yet been recognized, which include deferred revenue from open contracts and the amounts that will be invoiced and recognized as revenues in future periods. Remaining performance obligations represent the transaction price of firm orders for which service has not been performed and excludes unexercised renewals. The Company applied the short-term contract exemption to exclude the remaining performance obligations that are part of a contract that has an original expected duration of one year or less. From time to time, the Company enters into contracts with customers that extend beyond one year, with certain of its customers electing to pay for more than one year of services upon contract execution. For any discounts associated with these multiple year contracts, the Company concluded our contracts did not contain a financing component. Revenues by sales channel are as follows (in thousands): Year Ended December 31, 2018 ASC 606 Revenue Operating Lease Revenue Total Revenue Direct $ 148,310 $ 15,774 $ 164,084 Partner 106,816 7,989 114,805 Total $ 255,126 $ 23,763 $ 278,889 Prior periods have not been adjusted under the modified retrospective method. Year Ended December 31, 2017 ASC 605 Revenue Operating Lease Revenue Total Revenue Direct $ 124,355 $ 15,484 $ 139,839 Partner 84,370 6,619 90,989 Total $ 208,725 $ 22,103 $ 230,828 The Company utilizes partners to enable and accelerate the adoption of its cloud platform by increasing its distribution capabilities and market awareness of its cloud platform as well as by targeting geographic regions outside the reach of its direct sales force. The Company's channel partners maintain relationships with their customers throughout the territories in which they operate and provide their customers with services and third-party solutions to help meet those customers’ evolving security and compliance requirements. As such, these partners may offer the Company's IT security and compliance solutions in conjunction with one or more of their own products or services and act as a conduit through which the Company can connect with these prospective customers to offer its solutions. For sales involving a channel partner, the channel partner engages with the prospective customer directly and involves the Company's sales team as needed to assist in developing and closing an order. When a channel partner secures a sale, the Company sells the associated subscription to the channel partner who in turn resells the subscription to the customer. Sales to channel partners are made at a discount and revenues are recorded at this discounted price over the subscription terms. The Company does not have any influence or specific knowledge of its partners' selling terms with their customers. See Note 11, "Segment Information and Information about Geographic Area" for disaggregation of revenue by geographic area.

Business Combination (Notes)

Business Combination (Notes)	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Business Combination	Business Combinations On October 16, 2018, the Company completed the acquisition of Layered Insight ("Layered Insight"), a pioneer and global leader in container native application protection, providing accurate insight into container images, adaptive analysis of running containers, and automated enforcement of the container environment. Total consideration related to the acquisition was $13.4 million , of which $1.6 million is payable in the future subject to terms and conditions of the purchase agreement. All consideration is payable in cash. The Company also agreed to pay up to an additional $4.0 million if the acquired business achieves certain revenue milestones for the annual period ending December 31, 2019. The estimated fair value of these milestone payments was determined based on management’s estimate of fair value using a Monte Carlo simulation model, which uses Level 3 inputs for fair value measurements. This contingent consideration was included in the component of the purchase price and has been recorded as accrued liabilities in the accompanying consolidated balance sheet as of December 31, 2018 for $1.5 million . In addition to the prior milestone, shareholders of Layered Insight will receive $4.0 million in future payments if certain key employees continue their employment with the Company through December 31, 2019. The second milestone is being accounted for as post combinations services and is being expensed into our consolidated statement of income. The Company accounted for this acquisition as a business combination and allocated $9.6 million of the purchase price to technology-based intangible assets and $5.4 million to goodwill. The acquired intangible asset relating to Layered Insight's developed technology is being amortized over the estimated useful life of approximately four years. Goodwill arising from the Layered Insight acquisition is not deductible for tax purposes. On April 1, 2018, the Company acquired the assets of 1Mobility Private Limited ("1Mobility"), a Singapore-based company. The acquisition allows the Company to provide enterprises of all sizes with the ability to create and continuously update an inventory of mobile devices on all versions of Android, iOS and Windows Mobile in their environment; and to continuously assess their security and compliance posture, while quarantining devices that are compromised or out-of-compliance. Total purchase consideration was $4.0 million , of which $0.6 million is payable in the future subject to terms and conditions of the purchase agreement. The Company accounted for this transaction as a business combination and allocated $3.7 million of the purchase price to technology-based intangible assets and $0.3 million to goodwill. The acquired intangible assets relating to 1Mobility's developed technology are being amortized over the estimated useful lives of approximately four years. Goodwill arising from the 1Mobility acquisition is deductible for tax purposes over 15 years. The allocation of the consideration for business combinations completed in 2018 is summarized as follows (in thousands): Acquiree Purchase Consideration Net Tangible Assets Acquired/ (liabilities assumed) Purchased Intangible Assets Goodwill Deferred Tax Liability 1Mobility $ 4,000 $ — $ 3,700 $ 300 $ — Layered Insight $ 13,434 $ 80 $ 9,600 $ 5,376 $ (1,622 ) In 2017, the Company purchased certain assets of Nevis Networks (India) Private Limited (“Nevis”) and Defensative, LLC (NetWatcher). The Nevis acquisition accelerates the Company's development of network security solutions for detection and awareness of external intrusions to computer networks. The NetWatcher acquisition expands the Company's threat protection and management capabilities and adds new offerings to managed security service providers. Total purchase consideration related to the Company’s business combinations was $5.8 million in cash for Nevis, and $7.7 million for NetWatcher of which $1.0 million is payable in the future subject to terms and conditions of the purchase agreement. Total cash paid in the business combinations completed during 2017 was $12.5 million . Pro forma financial information for these acquisitions have not been presented because they are not material to our consolidated financial statements, either individually or in aggregate. In connection with the NetWatcher acquisition, certain founders of NetWatcher will receive future payments with continued employment at their one year and two -year anniversaries with the Company. These future payments are being recorded as employee compensation expense ratably over the two-year period. The Company accounted for the acquisition of certain assets of Nevis and Netwatcher as business combinations. The allocation of the consideration for business combinations completed in the year of 2017 is summarized as follows (in thousands): Acquiree Purchase Consideration Net Tangible Assets Acquired/ (liabilities assumed) Purchased Intangible Assets Goodwill Nevis $ 5,753 $ 14 $ 5,156 $ 583 NetWatcher 7,729 80 7,000 649 Total $ 13,482 $ 94 $ 12,156 $ 1,232 Purchased intangible assets represent the estimated fair value of purchased technology from our acquisitions of Nevis and NetWatcher. The excess of purchase consideration over the fair value of net tangible and identifiable intangible assets acquired was recorded as goodwill. Goodwill generated from these acquisitions was primarily related to the acquired workforce, expected improvements in technology performance and additional product functionality. The fair values assigned to tangible assets acquired and identifiable intangible assets are based on management's estimates and assumptions. The intangible assets have an estimated useful life of 5 years. Goodwill is deductible for tax purposes over 15 years. On January 10, 2019, the Company acquired certain assets of Adya, Inc. ("Adya"), a Delaware corporation. Adya’s technology expands the Company's solutions to help customers administer their critical SaaS applications from one console, save costs on SaaS licenses, set and enforce security policies in one place, and report and audit on all activity with a single tool. The purchase consideration related to the acquisition was $1 million in cash, in addition to $0.2 million and $0.6 million that is payable in the future subject to terms and conditions of the purchase agreement. The acquisition will be accounted for as an asset purchase.

Goodwill and Intangible Assets,

Goodwill and Intangible Assets, Net	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets Disclosure [Text Block]	NOTE 6. Goodwill and Intangible Assets, Net Intangible assets consist primarily of developed technology and patent licenses in business combinations. Acquired intangibles are amortized on a straight-line basis over the respective estimated useful lives of the assets. During the year ended December 31, 2018, the Company acquired 1Mobility and Layered Insight. These acquisitions resulted in an increase of developed technology intangible assets of $3.7 million and $9.6 million , respectively. The carrying values of intangible assets as of December 31, 2018 are as follows (in thousands): December 31, 2018 Weighted Average Lives Weighted Remaining Average Lives Cost Accumulated Amortization Net Book Value Developed technology 5 years 4 years $ 25,456 $ (4,085 ) $ 21,371 Patent licenses 14 years 6 years 1,387 (822 ) 565 Total intangibles subject to amortization $ 26,843 $ (4,907 ) 21,936 Intangible assets not subject to amortization 40 Total intangible assets, net $ 21,976 December 31, 2017 Weighted Average Lives Weighted Remaining Average Lives Cost Accumulated Amortization Net Book Value Developed technology 5 years 5 years $ 14,067 $ (2,371 ) $ 11,696 Patent licenses 14 years 7 years 1,388 (723 ) 665 Total intangibles subject to amortization $ 15,455 $ (3,094 ) 12,361 Intangible assets not subject to amortization 40 Total intangible assets, net $ 12,401 Intangible assets amortization expense was $3.7 million and $0.7 million for 2018 and 2017 , respectively. As of December 31, 2018 , the Company expects amortization expense in future periods to be as follows (in thousands): 2019 $ 5,856 2020 5,856 2021 5,856 2022 4,202 2023 100 2024 and thereafter 66 Total expected future amortization expense $ 21,936 Goodwill, which is not subject to amortization, totaled $7.2 million and $1.5 million as of December 31, 2018 , and 2017 , respectively. Changes in the carrying amount of goodwill for the years ended December 31, 2018, 2017 and 2016 were as follows (in thousands): Amount Balance as of December 31, 2016 $ 317 Goodwill acquired 1,232 Balance as of December 31, 2017 1,549 Goodwill acquired 5,676 Balance as of December 31, 2018 $ 7,225

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	NOTE 7. Commitments and Contingencies Leases The Company leases certain computer equipment and its corporate office and data center facilities under non-cancelable operating leases for varying periods through 2028. The following are the minimum annual lease payments due under operating leases at December 31, 2018 (in thousands): 2019 8,173 2020 7,284 2021 6,046 2022 4,538 2023 4,298 2024 and thereafter 19,299 Total minimum lease payments $ 49,638 Rent expense was $9.9 million , $9.6 million and $7.1 million for 2018 , 2017 and 2016 , respectively. Although certain of the operating lease agreements provide for rent free periods or escalating rent payments over the terms of the leases, rent expense under these agreements is recognized on a straight-line basis over the term of the lease, starting when the Company takes possession of the property from the landlord. As of December 31, 2018 and 2017 , the Company has accrued $10.8 million and $9.5 million of deferred rent related to these agreements, which is reflected in accrued liabilities and other noncurrent liabilities in the accompanying consolidated balance sheets. On October 14, 2016, the Company entered into a lease agreement (included in the table above) for its new headquarters office facility. The lease payments commenced on May 1, 2018 and the lease has a ten -year term through April 30, 2028. The remaining total commitment as of December 31, 2018 is $36.4 million and is payable monthly with escalating rental payments throughout the lease term. In connection with this lease, the Company provided the landlord with a $1.2 million standby letter of credit to secure the Company’s obligations through the end of the lease term, which was classified as restricted cash in the accompanying consolidated balance sheets. Indemnifications The Company from time to time enters into certain types of contracts that contingently require it to indemnify various parties against claims from third parties. These contracts primarily relate to (i) the Company's by-laws, under which it must indemnify directors and executive officers, and may indemnify other officers and employees, for liabilities arising out of their relationship, (ii) contracts under which the Company must indemnify directors and certain officers for liabilities arising out of their relationship, and (iii) contracts under which the Company may be required to indemnify customers or resellers from certain liabilities arising from potential infringement of intellectual property rights, as well as potential damages caused by limited product defects. To date, the Company has not incurred and has not recorded any liability in connection with such indemnifications. The Company maintains director and officer insurance, which may cover certain liabilities arising from its obligation to indemnify its directors. Contingencies The Company regularly licenses technology from various third party licensors. From time to time, the Company is audited by its licensors for compliance with the terms of the license agreements. During the quarter ended March 31, 2018, the Company commenced discussions with one of its vendors with respect to compliance with the terms of the applicable license agreement. During the three months ended June 30, 2018, the audit was completed and the Company reached a resolution with its licensor. Management sufficiently accrued for licensing agreement matters in the first quarter of 2018 and for the year ended December 31, 2018.

Employee Stock and Benefit Plan

Employee Stock and Benefit Plans	12 Months Ended
	Dec. 31, 2018
Share-based Compensation [Abstract]
Employee Stock and Benefit Plans	NOTE 8. Stockholders' Equity and Stock-based Compensation Common Stock The Company had reserved shares of common stock for future issuance as of December 31, 2018 as follows: Options and RSUs outstanding under equity incentive plans 2000 Equity Incentive Plan 244,652 2012 Equity Incentive Plan 4,477,717 Shares available for future grants under an equity incentive plan 2012 Equity Incentive Plan 3,817,097 Total shares reserved for future issuance 8,539,466 Preferred Stock Effective October 3, 2012, the Company is authorized to issue 20,000,000 shares of undesignated preferred stock with a par value of $0.001 per share. Each series of preferred stock will have such rights and preferences including dividend rights, dividend rate, conversion rights, voting rights, rights and terms of redemption (including sinking fund provisions), redemption price, and liquidation preferences as determined by the Board. As of December 31, 2018, and 2017, there were no issued or outstanding shares of preferred stock. Stock Options 2012 Equity Incentive Plan The 2012 Equity Incentive Plan (the 2012 Plan) was adopted and approved in September 2012 and became effective on September 26, 2012. Under the 2012 Plan, the Company is authorized to grant to eligible participant's incentive stock options (ISOs), non-statutory stock options (NSOs), stock appreciation rights (SARs), restricted stock awards (RSAs), restricted stock units (RSUs), performance units and performance shares equivalent to up to 11,791,179 shares of common stock as of December 31, 2018 . The number of shares of common stock available for issuance under the 2012 Plan includes an annual increase on January 1 of each year by an amount equal to the least of 3,050,000 shares; 5% of the outstanding shares of stock as of the last day of the immediately preceding fiscal year; or an amount determined by the Board of Directors. Options may be granted with an exercise price that is at least equal to the fair market value of the Company's stock at the date of grant and are exercisable when vested. Options granted generally vest over a period of up to four years, with a maximum term of ten years. ISOs may only be granted to employees and any subsidiary corporations' employees. All other awards may be granted to employees, directors and consultants and subsidiary corporations' employees and consultants. Options, SARs, RSUs, performance units and performance awards may be granted with vesting terms as determined by the Board of Directors and expire no more than ten years after the date of grant or earlier if employment or service is terminated. As of December 31, 2018 , 3,817,097 shares were available for grant under the 2012 Plan. 2000 Equity Incentive Plan Under the 2000 Equity Incentive Plan (the 2000 Plan), the Company was authorized to grant to eligible participants either ISOs or NSOs. The ISOs were granted at a price per share not less than the fair market value at the date of grant. The NSOs were granted at a price per share not less than 85% of the fair market value at the date of grant. Options granted generally vest over a period of up to four years, with a maximum term of ten years. The 2000 Plan was terminated in connection with the closing of the IPO, and accordingly, no shares are currently available for issuance under the 2000 Plan. The 2000 Plan continues to govern outstanding awards granted thereunder. Options granted under the 2000 Plan were immediately exercisable, and unvested shares are subject to repurchase by the Company. Upon termination of employment of an option holder, the Company has the right to repurchase at the original purchase price any issued but unvested common shares. The amounts paid for shares purchased under an early exercise of stock options and subject to repurchase by the Company are not reported as a component of stockholders ’ equity (deficit) until those shares vest. The amounts received in exchange for these shares are recorded as an accrued liability in the accompanying consolidated balance sheets and will be reclassified to common stock and additional paid-in capital as the shares vest. Stock-based Compensation Stock-based compensation included in the consolidated statements of operations is as follows: Year Ended December 31, 2018 2017 2016 (in thousands) Cost of revenues $ 2,489 $ 2,159 $ 1,858 Research and development 7,961 5,944 5,678 Sales and marketing 4,650 4,755 4,870 General and administrative 14,990 14,103 7,743 Total stock-based employee compensation $ 30,090 $ 26,961 $ 20,149 Stock-based compensation cost is recognized on a straight-line basis over the service period. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures materially differ from those estimates. As of December 31, 2018 , the Company had $13.8 million of total unrecognized employee compensation cost related to unvested options that it expects to recognize over a weighted-average period of 2.1 years. The fair value of each option granted to employees is estimated on the date of grant using the Black-Scholes-Merton option-pricing model based on the following assumptions: Year Ended December 31, 2018 2017 2016 Expected term (in years) 4.5 to 5.0 5.1 to 5.5 5.0 to 5.9 Volatility 45% to 47% 47% to 49% 45% to 49% Risk-free interest rate 2.5% to 3.0% 1.8% to 2.0% 1.1% to 1.3% Dividend yield — — — The expected term of the options is based on evaluations of historical and expected future employee exercise behavior. The risk-free interest rate is based on the U.S. Treasury rates at the date of grant with maturity dates approximately equal to the expected term at the grant date. Prior to the third quarter of 2017, volatility was based on a combination of the historical volatility of the Company and of several public entities that are similar to the Company. The Company based volatility on this combination because it did not have sufficient historical transactions in its own shares on which to solely base expected volatility. Beginning in the third quarter of 2017, the volatility was estimated using the historical volatility derived from the Company's common stock. The Company has not historically declared any dividends and does not expect to in the future. Non-Employee Stock-based Compensation The Company records compensation representing the fair value of stock options granted to non-employees. Stock-based non-employee compensation was $0.4 million , $0.9 million and $0.7 million for 2018 , 2017 and 2016 , respectively. Non-employee stock-based compensation is recognized over the vesting periods of the options. The value of options granted to non-employees is re-measured as they vest over a performance period. Stock Option Plan Activity A summary of the Company’s stock option activity is as follows: Outstanding Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Life (Years) Aggregate Intrinsic Value (in thousands) Balance as of December 31, 2015 7,579,058 $ 16.88 5.9 $ 131,345 Granted 2,120,633 $ 26.64 Exercised (1,399,157 ) $ 10.83 Canceled (772,854 ) $ 31.57 Balance as of December 31, 2016 7,527,680 $ 19.25 6.0 $ 101,717 Granted 408,225 $ 40.82 Exercised (2,997,095 ) $ 11.05 Canceled (442,919 ) $ 33.29 Balance as of December 31, 2017 4,495,891 $ 25.29 6.6 $ 153,129 Granted 366,786 $ 79.79 Exercised (1,183,235 ) $ 20.33 Canceled (250,133 ) $ 39.61 Balance as of December 31, 2018 3,429,309 $ 31.79 6.4 $ 149,935 Vested and expected to vest - December 31, 2018 3,230,498 $ 30.27 6.2 $ 145,521 Exercisable - December 31, 2018 2,459,936 $ 25.27 5.7 $ 121,696 The following table summarizes the outstanding and vested stock options at December 31, 2018 : Outstanding Exercisable Exercise Price Number of Weighted Weighted Number of Weighted $2.80 - $12.68 376,405 $ 8.58 3.1 376,405 $ 8.58 $13.50 - $25.17 474,527 $ 21.70 5.4 412,956 $ 21.18 $25.56 - $25.56 886,676 $ 25.56 7.3 587,978 $ 25.56 $26.86 - $26.86 427,997 $ 26.86 5.1 427,997 $ 26.86 $30.58 - $34.97 372,331 $ 31.78 6.2 307,743 $ 31.54 $36.25 - $40.15 391,568 $ 37.78 7.2 225,200 $ 37.53 $40.68 - $59.95 213,744 $ 49.97 7.6 121,460 $ 45.16 $76.21 - $76.21 101,125 $ 76.21 9.8 — $ — $78.85 - $78.85 78,550 $ 78.85 9.3 93 $ 78.85 $95.10 - $95.10 106,386 $ 95.10 9.5 104 $ 95.10 3,429,309 $ 31.79 6.4 2,459,936 $ 25.27 The weighted-average grant date fair value of the Company’s stock options granted during 2018 , 2017 and 2016 was $33.05 , $18.03 and $11.12 , respectively. The aggregate grant date fair value of the Company’s stock options granted during 2018 , 2017 and 2016 was $12.1 million , $7.4 million and $23.6 million , respectively. The intrinsic value of options exercised was $71.7 million , $92.1 million and $25.0 million during 2018 , 2017 and 2016 , respectively. Intrinsic value of an option is the difference between the fair value of the Company’s common stock at the time of exercise and the exercise price paid. Restricted Stock The terms and conditions of RSUs include vesting criteria and timing are set by the Board of Directors. The cost of RSUs is determined using the fair value of the Company’s common stock on the date of the grant. Compensation cost is recognized on a straight-line basis over the requisite service period of each grant adjusted for estimated forfeitures. A summary of the Company’s RSU activity is as follows: Number of Shares Weighted-Average Grant Date Fair Value Per Share Balance as of December 31, 2015 47,500 $ 37.28 Granted 681,350 $ 28.52 Vested (39,998 ) $ 27.49 Cancelled (101,519 ) $ 31.12 Balance as of December 31, 2016 587,333 $ 28.85 Granted 1,326,849 $ 42.69 Vested (368,367 ) $ 33.52 Cancelled (135,227 ) $ 32.04 Balance as of December 31, 2017 1,410,588 $ 40.34 Granted 548,245 $ 75.44 Vested (525,375 ) $ 39.87 Cancelled (206,575 ) $ 43.43 Balance as of December 31, 2018 1,226,883 $ 55.71 Outstanding and expected to vest - December 31, 2018 898,637 $ 54.67 As of December 31, 2018 , the Company had $54.3 million of unrecognized compensation cost related to unvested awards that it expects to recognize over a weighted-average period of 2.7 years. On December 21, 2018, the Board of Directors granted an award of time-based and performance-based restricted stock units to the Company’s Chairman and Chief Executive Officer, Philippe Courtot. The compensation committee of the Board, in consultation with its independent compensation consultant, designed these awards so that greater than 50% of this compensation was based on the achievement of performance goals linked to metrics designed to drive the creation of shareholder value. The first portion of the award consists of 56,250 time-based stock restricted stock units that will vest in 16 quarterly increments beginning on January 1, 2019, assuming continued service through each applicable vesting date. The second portion of the award consists of 33,089 performance-based restricted stock units that vest based on achievement of goals related to revenue growth for a three -year period from January 2019 through December 2021 and adjusted EBITDA margin for the 2021 fiscal year, generally conditioned on Mr. Courtot’s continued status as a service provider through the date that performance is certified. The third portion of the award consists of 33,088 performance-based restricted stock units that will vest in 3 increments based on the achievement of goals related to revenue growth and adjusted EBITDA margin for each of the 2019, 2020, and 2021 fiscal years, generally conditioned on Mr. Courtot’s continued status as a service provider through the date that performance is certified for the relevant increment. If Mr. Courtot’s employment (a) is terminated by reason of death or disability or (b) is terminated by the Company for reasons other than cause or good reason within 12 months following a change in control (a “double trigger” termination), then 100% of any unvested portions of the award will vest, with any vesting in connection with change in control terminations conditioned upon the effectiveness of a release of claims in favor of the Company. The Company will account for these awards as share-based compensation with multiple performance conditions. and will recognize compensation cost when it is probable that the performance conditions are met. The Company will assess these conditions on a quarterly basis. As of December 31, 2018, no stock-based compensation cost for these awards has been recognized. Share Repurchase Program On February 5, 2018, the Company's Board of Directors authorized a $100.0 million two-year share repurchase program, which was announced on February 12, 2018. The Company's share repurchases may be effected from time to time through open market purchases. Repurchased shares are retired and reclassified as authorized and unissued shares of common stock. On retirement of the repurchased shares, common stock is reduced by an amount equal to the number of shares being retired multiplied by the par value. The excess of the cost of treasury stock that is retired over its par value is first allocated as a reduction to additional paid-in capital based on the initial public offering price of the stock, with the remaining excess to retained earnings. On October 25, 2018, the Company's Board of Directors authorized an additional $100.0 million two-year share repurchase program, which was announced on October 30, 2018. During the year ended December 31, 2018 , the Company repurchased 1,088,899 shares of its common stock for approximately $85.0 million . All share repurchases were made using cash resources. As of December 31, 2018 , approximately $115.0 million remained available for share repurchases pursuant to the Company's share repurchase program. 401(k) Plan The Company’s 401(k) Plan (the “401(k) Plan”) was established in 2000 to provide retirement and incidental benefits for its employees. As allowed under section 401(k) of the Internal Revenue Code, the 401(k) Plan provides tax-deferred salary deductions for eligible employees. Contributions to the 401(k) Plan are limited to a maximum amount as set periodically by the Internal Revenue Service. During the years ended December 31, 2018, 2017 and 2016, the Company made contributions to the 401(k) Plan of $1.2 million , and $1.1 million , respectively.

Other Income (Expense), Net

Other Income (Expense), Net	12 Months Ended
	Dec. 31, 2018
Other Income and Expenses [Abstract]
Other Income (Expense), Net	NOTE 9. Other Expense, Net Other expense, net consists of the following: Year Ended December 31, 2018 2017 2016 (in thousands) Foreign exchange losses $ (577 ) $ (355 ) $ (770 ) Other expense (224 ) (181 ) (202 ) Other expense, net $ (801 ) $ (536 ) $ (972 )

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	NOTE 10. Income Taxes The Company’s geographical breakdown of income before income taxes is as follows: Year Ended December 31, 2018 2017 2016 (in thousands) Domestic $ 50,010 $ 34,914 $ 28,982 Foreign 5,458 4,464 1,447 Income before income taxes $ 55,468 $ 39,378 $ 30,429 The provision for (benefit from) income taxes consists of the following: Year Ended December 31, 2018 2017 2016 (in thousands) Current Federal $ (90 ) $ 22 $ 8,334 State 62 23 1,125 Foreign 1,988 1,471 963 Total current provision 1,960 1,516 10,422 Deferred Federal (3,449 ) (1,650 ) 611 State 21 (996 ) 126 Foreign (368 ) 68 46 Total deferred (benefit) provision (3,796 ) (2,578 ) 783 Total (benefit from) provision for income taxes $ (1,836 ) $ (1,062 ) $ 11,205 The reconciliation of the statutory federal income tax rate to the Company’s effective tax rate is as follows: Year Ended December 31, 2018 2017 2016 Federal statutory rate 21.0 % 35.0 % 35.0 % State taxes (1.9 ) (2.1 ) 2.1 Stock-based compensation (20.4 ) (58.1 ) 2.4 Foreign source income (0.2 ) (0.2 ) 0.9 Change in valuation allowance 4.4 2.8 1.3 Federal rate adjustment (due to 2017 Tax Act) — 26.4 — Federal and state research and development credit (6.7 ) (5.3 ) (3.6 ) Other 0.5 (1.2 ) (1.3 ) (Benefit from) provision for income taxes (3.3 )% (2.7 )% 36.8 % On December 22, 2017, the Tax Cuts and Jobs Act (the “2017 Tax Act”) was enacted into law. The new legislation contains several key tax provisions that impact the Company, including the reduction of the corporate income tax rate from 35% to 21% effective January 1, 2018. The new legislation also includes a variety of other changes, such as a one-time repatriation tax on accumulated foreign earnings (transition tax), acceleration of business asset expensing, and reduction in the amount of executive pay that could qualify as a tax deduction, among others. The Company recognized a provisional income tax expense of $10.4 million in the fourth quarter of 2017, from the re-measurement of certain deferred tax assets and liabilities as a result of the reduction of the federal tax rate, which was included as a component of the income tax provision on our consolidated statement of income. The Company completed its analysis of the impacts of the 2017 Tax Act in the fourth quarter of 2018 with no material change to its provisional estimate. Deferred Income Taxes Deferred income taxes reflect the tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. The components of the Company’s deferred tax assets and liabilities are as follows: December 31, 2018 2017 (in thousands) Deferred tax assets Net operating loss carryforwards $ 11,250 $ 8,947 Research and development credit carryforwards 16,901 11,493 Foreign tax credit carryforwards 2,209 1,149 Accrued liabilities 2,723 1,470 Deferred revenues 4,200 3,416 Intangible assets — 405 Stock-based compensation 6,975 7,135 Other 174 196 Gross deferred tax assets 44,432 34,211 Valuation allowance (9,100 ) (5,773 ) Net deferred tax assets 35,332 28,438 Deferred tax liabilities Fixed assets (8,161 ) (3,372 ) Intangible assets (784 ) — Total deferred tax liabilities (8,945 ) (3,372 ) Net deferred tax assets $ 26,387 $ 25,066 The realization of deferred tax assets is dependent upon the generation of sufficient taxable income of the appropriate character in future periods. The Company regularly assesses the ability to realize its deferred tax assets and establishes a valuation allowance if it is more-likely-than-not that some portion, or all, of the deferred tax assets will not be realized. The Company weighs all available positive and negative evidence, including its earnings history and results of recent operations, scheduled reversals of deferred tax liabilities, projected future taxable income, and tax planning strategies. Due to the weight of objectively verifiable negative evidence, it is more-likely-than-not that its California deferred tax assets will not be realized as of December 31, 2018. Additionally, due to a lack of sufficient future income of the appropriate character, certain U.S. federal and state deferred tax assets are not more-likely-than-not to be realized. Accordingly, the Company has recorded a valuation allowance of $9.1 million against such deferred tax assets. The valuation allowance increased by $3.3 million and $2.1 million during the years ended December 31, 2018 and 2017, respectively. At December 31, 2018, the Company had federal and state net operating loss carryforwards of approximately $48.4 million and $14.0 million , respectively, available to reduce federal and state taxable income. Federal net operating losses begin to expire in 2021 , and state net operating losses begin to expire in 2022 . Utilization of the Company’s net operating loss carryforwards may be subject to an annual limitation due to the ownership change limitations provided by the Internal Revenue Code and similar state provisions. Such an annual limitation could result in the expiration of the net operating loss carryforwards before utilization. As of December 31, 2018, the Company had $12.2 million of federal and $10.9 million of state research and development credit carryforwards, respectively. Federal research and development credits begin to expire in 2022 . State research and development credits do not expire. As of December 31, 2018, the Company had foreign tax credit carryforwards of $2.2 million which begin to expire in 2024 . The following table summarizes the activity related to the Company’s unrecognized tax benefits: Year Ended December 31, 2018 2017 2016 Unrecognized tax benefits beginning balance $ 5,112 $ 4,071 $ 3,506 Gross increase for tax positions of prior years 279 66 2 Gross decrease for tax positions of prior years (227 ) — (15 ) Gross increase for tax positions of current year 1,399 1,101 659 Lapse of statute of limitations (157 ) (126 ) (81 ) Total unrecognized tax benefits $ 6,406 $ 5,112 $ 4,071 The unrecognized tax benefits, if recognized, would impact the income tax provision by $3.5 million , $2.8 million and $2.4 million as of December 31, 2018 , 2017 and 2016 , respectively. The remaining amount would be offset by the reversal of related deferred tax assets which are subject to a full valuation allowance. As of December 31, 2018, the Company does not believe that its estimates, as otherwise provided for, on such tax positions will significantly increase or decrease within the next twelve months. The Company has elected to include interest and penalties as a component of income tax expense. The amounts were not material for 2018, 2017 and 2016. The Company files income tax returns in the United States, including various state jurisdictions. The Company’s subsidiaries file tax returns in various foreign jurisdictions. The tax years 2001 through 2018 remain open to examination by the major taxing jurisdictions in which the Company is subject to tax. As of December 31, 2018, the Company was not under examination by the Internal Revenue Service, foreign, or any major state tax jurisdiction. U.S. income tax has not been recognized on the excess of the amount for financial reporting over the tax basis of investments in foreign subsidiaries that is indefinitely reinvested outside the United States. A determination of the unrecognized deferred tax liability related to this basis difference is not practicable because of the complexities of the calculation.

Segment Information and Informa

Segment Information and Information about Geographic Area	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Segment Information and Information about Geographic Area	NOTE 11. Segment Information and Information about Geographic Area The Company operates in one segment. The Company’s chief operating decision maker is the Chairman, President and Chief Executive Officer, who makes operating decisions, assesses performance and allocates resources on a consolidated basis. All of the Company’s principal operations and decision-making functions are located in the United States. Revenues by geographic area, based on the location of the customer, are as follows: Year Ended December 31, 2018 2017 2016 (in thousands) United States $ 185,887 $ 162,681 $ 139,743 Foreign 93,002 68,147 58,182 Total revenues $ 278,889 $ 230,828 $ 197,925 Property and equipment, net, by geographic area, are as follows: December 31, 2018 2017 (in thousands) United States $ 59,222 $ 50,785 Foreign 2,220 7,772 Total property and equipment, net $ 61,442 $ 58,557

Net Income Per Share Attributab

Net Income Per Share Attributable to Common Stockholders	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Net Income Per Share Attributable to Common Stockholders	NOTE 12. Net Income Per Share The computations for basic and diluted net income per share are as follows: Year Ended December 31, 2018 2017 2016 (in thousands, except per share data) Numerator: Net income - basic and diluted $ 57,304 $ 40,440 $ 19,224 Denominator: Weighted-average shares used in computing net income per share - basic 38,876 37,443 35,247 Effect of potentially dilutive securities: Common stock options 2,401 2,262 3,052 RSUs 620 366 70 Weighted-average shares used in computing net income per share - diluted 41,897 40,071 38,369 Net income per share: Basic $ 1.47 $ 1.08 $ 0.55 Diluted $ 1.37 $ 1.01 $ 0.50 Potentially dilutive securities not included in the calculation of diluted net income per share because doing so would be anti-dilutive are as follows: Year Ended December 31, 2018 2017 2016 (in thousands) Common stock options 177 742 3,241 RSUs 22 71 24

Quarterly Financial Information

Quarterly Financial Information (Unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information (Unaudited)	NOTE 13. Selected Quarterly Financial Information (Unaudited) The following table shows a summary of the Company's quarterly financial information for each of the quarters in the two-year period ended December 31, 2018 : Three Months Ended Mar. 31, 2017 Jun. 30, 2017 Sep. 30, 2017 Dec. 31, 2017 Mar. 31, 2018 Jun. 30, 2018 Sep. 30, 2018 Dec. 31, 2018 (unaudited) (in thousands, except per share data) Revenues $ 53,121 $ 55,302 $ 59,490 $ 62,915 $ 64,878 $ 68,153 $ 71,658 $ 74,200 Income from operations 7,656 9,009 10,849 9,729 8,406 10,895 18,117 12,943 Other income, net 453 360 671 652 1,245 884 1,116 1,862 Income before income taxes 8,109 9,369 11,520 10,381 9,651 11,779 19,233 14,805 Net income 21,930 7,202 8,452 2,857 9,142 10,293 23,469 14,400 Net income per share: Basic $ 0.60 $ 0.19 $ 0.22 $ 0.07 $ 0.24 $ 0.26 $ 0.60 $ 0.37 Diluted $ 0.56 $ 0.18 $ 0.21 $ 0.07 $ 0.22 $ 0.24 $ 0.56 $ 0.35

Schedule II Schedule of Valuati

Schedule II Schedule of Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2018
Valuation and Qualifying Accounts [Abstract]
Schedule II Schedule of Valuation and Qualifying Accounts	SCHEDULE II SUPPLEMENTARY CONSOLIDATED FINANCIAL STATEMENT SCHEDULE VALUATION AND QUALIFYING ACCOUNTS (in thousands) Additions Balance at Beginning of Year Charged to Costs and Expenses Deductions and Other (1) Balance at End of Year Allowance for Doubtful Accounts Year Ended December 31, 2018 $ 816 $ 85 $ (218 ) $ 683 Year Ended December 31, 2017 $ 702 $ 657 $ (543 ) $ 816 Year Ended December 31, 2016 $ 769 $ 199 $ (266 ) $ 702 (1) Primarily represents write-offs of uncollectible accounts, net of recoveries. All other schedules have been omitted because they are not required, not applicable, or the required information is otherwise included.

The Company and Summary of Si_2

The Company and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Description of Business	Description of Business Qualys, Inc. (the “Company”, "we", "us", "our") was incorporated in the state of Delaware on December 30, 1999. The Company is headquartered in Foster City, California and has wholly-owned subsidiaries throughout the world. The Company is a pioneer and leading provider of cloud-based security and compliance solutions that enable organizations to identify security risks to their IT infrastructures, help protect their IT systems and applications from ever-evolving cyber-attacks and achieve compliance with internal policies and external regulations. The Company’s cloud solutions address the growing security and compliance complexities and risks that are amplified by the dissolving boundaries between internal and external IT infrastructures and web environments, the rapid adoption of cloud computing and the proliferation of geographically dispersed IT assets. Organizations can use the Company’s integrated suite of solutions delivered on its Qualys Cloud Platform to cost-effectively obtain a unified view of their security and compliance posture across globally-distributed IT infrastructures.
Basis of presentation	Basis of Presentation The accompanying consolidated financial statements and footnotes have been prepared by the Company in accordance with accounting principles generally accepted in the United States (“U.S. GAAP”) as well as the instructions to Form 10-K and the rules and regulations of the U.S. Securities and Exchange Commission ("SEC"). In the opinion of management, the accompanying consolidated financial statements reflect all adjustments, which include only normal recurring adjustments, necessary for the fair presentation of the Company’s consolidated financial position, results of operations and cash flows for the periods presented. The accompanying consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All significant intercompany transactions and balances have been eliminated upon consolidation.
Use of estimates	Use of Estimates The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make certain estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of assets and liabilities at the date of the consolidated financial statements and the reported results of operations during the reporting period. The Company’s management regularly assesses these estimates, which primarily affect revenue recognition, the valuation of accounts receivable, goodwill and intangible assets, capitalization of internally developed software, stock-based compensation and the provision for income taxes. Actual results could differ from those estimates and such differences may be material to the accompanying consolidated financial statements.
Concentration of credit risk	Concentration of Credit Risk The Company invests its cash and cash equivalents with major financial institutions. Cash balances with any one institution at times may be in excess of federally insured limits. Cash equivalents are invested in high-quality investment grade financial instruments and are diversified. The Company has not experienced any losses in such accounts and believes it is not exposed to any significant credit risk. Credit risk with respect to accounts receivable is dispersed due to the large number of customers. Collateral is not required for accounts receivable. As of December 31, 2018 and 2017 , no customer or channel partner accounted for more than 10% of the Company's revenues and accounts receivable balance.
Cash, cash equivalents and short-term and long-term investments	Cash, Cash Equivalents, Short-Term and Long-Term Investments Cash and cash equivalents include cash held in banks, highly liquid money market funds, commercial paper, and fixed-income U.S. government agency securities, all with original maturities of three months or less when acquired. The Company’s investments consist of fixed-income U.S. government agency securities, corporate bonds, asset-backed securities and commercial paper. Management determines the appropriate classification of the Company's investments at the time of purchase and reevaluates such designation at each balance sheet date. The Company classifies its investments as either short-term or long-term based on each instrument's underlying contractual maturity date. Cash equivalents are stated at cost, which approximates fair market value. Short-term and long-term investments are classified as available-for-sale and are carried at fair value. Unrealized gains and losses in fair value are reported in other comprehensive income (loss). When the available-for-sale securities are sold, cost is based on the specific identification method, and the realized gains and losses are included in other income (expense) in the consolidated statements of operations. Short-term and long-term investments are reviewed quarterly for impairment that is deemed to be other-than-temporary. An investment is considered other-than-temporarily impaired when its fair value is below its amortized cost and (1) there is an intent to sell the security, (2) it is “more likely than not” that the security will be sold before recovery of its amortized cost basis or (3) the present value of expected cash flows from the investment is not expected to recover the entire amortized cost basis. Declines in value that are considered to be other-than-temporary and adjustments to amortized cost for the amortization of premiums and the accretion of discounts are recorded in other income (expense). Interest and dividends are recorded in interest income as earned.
Accounts receivable	Accounts Receivable Accounts receivable are recorded at the invoiced amount and do not bear interest. The allowance for doubtful accounts represents the Company’s best estimate of the amount of probable credit losses and is determined based on a review of existing accounts receivable by aging category to identify significant customers or invoices with collectability issues. For those invoices not specifically reviewed, the reserve is calculated based on the age of the receivable and historical write-offs. Any change in the assumptions used in analyzing a specific account receivable may result in an additional provision for doubtful accounts being recognized in the period in which the change occurs. When the Company ultimately concludes that a receivable is uncollectible, the balance is written off against the allowance for doubtful accounts. Payments subsequently received on such receivables are credited back to the allowance for doubtful accounts.
Cost method investments	Cost Method Investments In the second quarter of fiscal 2018, the Company invested $2.5 million in a privately-held company. The Company used the cost method of accounting to account for the investment because it does not hold a controlling interest in this entity and the Company does not have the ability to exercise significant influence over the entity's operating and financial policies. The investment is included in long term assets on the accompanying consolidated balance sheets. The Company's cost method investment is assessed for impairment when events or changes in circumstances indicate that the carrying amount may not be recoverable. The Company has not recorded any dividends or other-than-temporary impairment charges related to its cost method investment. The fair value of the investment is not readily available, and there are no quoted market prices for the investment.
Property and equipment, net	Property and Equipment, net Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation is computed using the straight-line method over the estimated useful lives of the assets, which range from three to five years. Leasehold improvements are amortized on a straight-line basis over the lesser of the estimated useful life of the asset or the lease term. The Company purchases physical scanner appliances and other computer equipment that are provided to customers on a subscription basis. This equipment is recorded within property and equipment on the accompanying consolidated balance sheet, and the depreciation is recorded to cost of revenues over an estimated useful life of three years. Upon retirement or disposal, the cost of assets and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is reflected in the consolidated statements of operations. Repairs and maintenance that do not extend the life of an asset are expensed as incurred and major improvements are capitalized as property and equipment.
Impairment of long-lived assets	Impairment of Long-Lived Assets The Company evaluates its long-lived assets, which consist of property and equipment, and intangible assets subject to amortization, for indicators of possible impairment when events or changes in circumstances indicate the carrying amount of an asset may not be recoverable. Impairment exists if the carrying amounts of such assets exceed the estimates of future undiscounted cash flows expected to be generated by such assets. Should an impairment exist, the impairment loss would be measured based on the excess carrying value of the asset over the asset’s estimated fair value. In each of 2018, 2017 and 2016, the Company had no impairment of long-lived assets.
Goodwill and intangible assets	Goodwill and Intangible Assets Goodwill represents the excess of the purchase price over the fair value of the net tangible and identifiable intangible assets acquired in a business combination and is not subject to amortization. Goodwill and other intangible assets with indefinite lives are not amortized, but tested for impairment annually or if certain circumstances indicate a possible impairment may exist. These tests are performed at the reporting unit level. The Company’s operations are organized as one reporting unit. In testing for a potential impairment of goodwill, the Company first performs a qualitative assessment of its reporting unit to determine if it is more likely than not (a more than 50% likelihood) that the fair value of the reporting unit is less than its carrying amount. If the fair value is not considered to be less than the carrying amount, no further evaluation is necessary. The Company performed the annual qualitative assessment for the year ended December 31, 2018 and concluded there was no potential impairment of goodwill. In testing for a potential impairment of intangible assets with indefinite lives that are not subject to amortization, the Company first performs a qualitative assessment to determine if it is more likely than not (a more than 50% likelihood) that the fair value of the indefinite-lived intangible assets is less than the carrying amount. If the fair value is not considered to be less than the carrying amount, no further evaluation is necessary. The Company performs the annual qualitative assessment in the fourth quarter each fiscal year. There were no such impairment losses during 2018, 2017 or 2016. If the qualitative assessment indicates there is more than a 50% likelihood that the fair value is less than the carrying amount of the reporting unit or the intangible asset, the Company would perform a two-step test. In the first step, the carrying value of the reporting unit or intangible asset is compared to its estimated fair value. If the estimated fair value is less than the carrying value, then potential impairment exists. In the second step, for goodwill, the Company calculates the amount of any impairment by determining the implied fair value of goodwill using a hypothetical purchase price allocation, similar to that which would be applied if it were an acquisition and the purchase price was equivalent to fair value as calculated in the first step. Impairment is equivalent to any excess of goodwill carrying value over its implied fair value. For indefinite-lived intangible assets, the Company performs the currently prescribed quantitative impairment test by comparing the fair value of the indefinite-lived intangible asset with its carrying value. Certain other intangible assets acquired are amortized over their estimated useful lives and tested for impairment if certain circumstances indicate an impairment may exist. The Company’s intangible assets are comprised primarily of existing technology, patent license, and non-competition agreements and are amortized over periods ranging from three to fourteen years on a straight-line basis. As of December 31, 2018 , the Company has not written down any of these intangible assets as a result of impairment.
Software development cost	Software Costs incurred in the development phase are capitalized and amortized over the product’s estimated useful life, which is three years. Capitalized costs include salaries, benefits, and stock-based compensation charges for employees that are directly involved in developing its cloud security platform during the post planning and implementation phases. Capitalized costs related to internally developed software under development are treated as construction in progress until the program, feature or functionality is ready for its intended use, at which time amortization commences. These capitalized costs are included in other noncurrent assets on the accompanying consolidated balance sheets.
Business combinations	Business Combinations We apply the provisions of ASC 805, Business Combinations, in accounting for our acquisitions. It requires us to recognize separately from goodwill the assets acquired and the liabilities assumed at their acquisition date fair values. Goodwill as of the acquisition date is measured as the excess of consideration transferred over the net of the acquisition date fair values of the assets acquired and the liabilities assumed. While we use our best estimates and assumptions to accurately value assets acquired and liabilities assumed at the acquisition date as well as any contingent consideration, where applicable, our estimates are inherently uncertain and subject to refinement. As a result, during the measurement period, which may be up to one year from the acquisition date, we record adjustments to the assets acquired and liabilities assumed with the corresponding offset to goodwill. Upon the conclusion of the measurement period or final determination of the values of assets acquired or liabilities assumed, whichever comes first, any subsequent adjustments are recorded to our consolidated statements of operations.
Derivative financial instruments	Derivative Financial Instruments Derivative financial instruments are utilized by the Company to reduce foreign currency exchange risks. The Company uses foreign currency forward contracts to mitigate the impact of foreign currency fluctuations of certain non-U.S. dollar denominated asset positions, to date primarily cash and accounts receivable (non-designated), as well as to manage foreign currency fluctuation risk related to forecasted transactions (designated). The Company accounts for these instruments as either non-designated or cash flow hedges, respectively. Open contracts are recorded within prepaid expenses and other current assets or accrued liabilities in the consolidated balance sheets. Gains and losses resulting from currency exchange rate movements on non-designated forward contracts are recognized in other income (expense). Any gains or losses from derivatives designated as cash flow hedges are first accumulated in other comprehensive income (AOCI) and then reclassified to revenue when the hedged item impacts the consolidated financial statements. During the year ended December 31, 2018, the Company began a hedging strategy to reduce its exposure to foreign currency exchange rate fluctuations for forecasted subscription renewals and new orders in both GBP and Euro. We use sell-forward currency contracts accounted for as cash flow hedges against a designated portion of forecasted subscription renewals and new orders . Upon executing a hedging contract and quarterly thereafter, the Company assesses hedge effectiveness using regression analysis. The Company includes time value in its effectiveness testing and the entire change in the value of hedge contracts was recorded as unrealized gains or losses in accumulated other comprehensive income (AOCI) within stockholders’ equity on the Company's consolidated balance sheet as of December 31, 2018. The unrealized gains or losses in AOCI will be reclassified into revenue when the respective hedged transactions affect earnings. As of December 31, 2018, the amount of unrealized gains and losses related to the hedged forecasted transactions reported in AOCI that is expected to be reclassified into revenue within the next 12 months was not material. The cash flow effects of the Company's derivative contracts for the year ended December 31, 2018 were included within net cash provided by operating activities on its consolidated statements of cash flows. The Company had notional amounts on foreign currency exchange contracts designated as cash flow hedges outstanding of €12.9 million and £4.1 million as of December 31, 2018. The unrealized FX losses on these contracts were recorded in AOCI and are insignificant. At December 31, 2018 , the Company had two outstanding non-designated forward contracts with notional amounts of €16.0 million and £6.3 million , respectively, both with the expiry date of January 31, 2019 . At December 31, 2017 , the Company had two non-designated outstanding forward contracts with notional amounts of €7.0 million and £4.8 million , which expired on January 31, 2018 . These forward contracts had insignificant fair value at both December 31, 2018 and 2017 . These derivatives were not designated as hedges. These instruments were valued using Level 2 inputs.
Share-based compensation	Stock-Based Compensation The Company recognizes the fair value of its employee stock options and restricted stock units (RSUs) over the requisite service period for those awards ultimately expected to vest. The fair value of each option is estimated on date of grant using the Black-Scholes-Merton option pricing model and the fair value of each restricted stock unit is based on the fair value of the Company's stock on the date of grant. Forfeitures are estimated on the date of grant and revised if actual or expected forfeiture activity differs materially from original estimates. Option grants to non-employees are accounted for at the fair value of the equity instrument issued, as calculated using the Black-Scholes-Merton option-pricing model and the expense is recognized over the vesting periods of the options. The value of options granted to non-employees is re-measured as they vest over a performance period.
Revenue recognition	Revenue Recognition The Company derives revenues from subscriptions that require customers to pay a fee in order to access the Company’s cloud solutions. Customers generally enter into one year renewable subscriptions though some customers do enter into subscriptions with longer terms. The subscription fee entitles the customer to an unlimited number of scans for a specified number of networked devices or web applications and, if requested by a customer as part of their subscription, a specified number of physical or virtual scanner appliances. Revenue is recognized when control of these subscription services is transferred to our customers, in an amount that reflects the consideration we expect to be entitled to in exchange for those services. The Company’s physical and virtual scanner appliances are requested by certain customers as part of their subscriptions in order to scan IT infrastructures within their firewalls and do not function without, and are not sold separately from, subscriptions for the Company’s solutions. In some limited cases, the Company also provides certain computer equipment used to extend its Qualys Cloud Platform into its customers’ private cloud environment. Customers are required to return physical scanner appliances and computer equipment if they do not renew their subscriptions.Physical equipment (scanners and private cloud platforms) are accounted for as operating leases and revenue is recognized over the subscription term. We determine revenue recognition through the following steps: • Identification of the contract, or contracts, with a customer; • Identification of the performance obligations in the contract; • Determination of the transaction price; • Allocation of the transaction price to the performance obligations in the contract; and • Recognition of revenue when, or as, we satisfy a performance obligation. At the inception of a customer contract, we make an assessment as to that customer's ability to pay for the services provided. We assess collectability based on a number of factors, including credit worthiness of the customer along with past transaction history. In addition, we perform periodic evaluations of our customers’ financial condition. The Company recognizes revenues for certain limited scan arrangements, for which expiration dates can be extended, on an as-used basis. Deferred revenues consist of customer contracts billed or cash received that will be recognized in the future under subscriptions existing at the balance sheet date. The current portion of deferred revenues represents amounts that are expected to be recognized within one year of the balance sheet date. Costs of shipping and handling charges incurred by the Company associated with physical scanner appliances and other computer equipment are included in cost of revenues. Sales taxes and other taxes collected from customers to be remitted to government authorities are excluded from revenues.
Advertising expenses	Advertising Expenses Advertising costs are expensed as incurred and include costs of advertising and promotional materials. The Company incurred advertising costs of $87 thousand , $482 thousand and $124 thousand for 2018 , 2017 and 2016 , respectively.
Income taxes	Income Taxes The Company provides for the effect of income taxes in its consolidated financial statements using the asset and liability method which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the consolidated financial statements. Under this method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases, net operating loss carryovers, and tax credit carry forwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in the period that includes the enactment date. Income tax expense or benefit is recognized for the amount of taxes payable or refundable for the current liabilities for the tax consequences of events that have been recognized in an entity’s financial statements or significant assumptions, judgments and estimates to determine its current provision (benefit) for income taxes, its deferred tax assets and liabilities, and any valuation allowance to be recorded against its deferred tax assets. The Company's judgments, assumptions and estimates relating to the current provision (benefit) for income taxes include the geographic mix and amount of income (loss), its possible outcomes of current and future audits conducted by foreign and domestic tax authorities. The anticipating the tax positions the Company will record in the consolidated financial statements before actually preparing and filing the tax returns. The Company's estimates and assumptions may differ from the actual results as reflected in its income tax required adjustments when they are identified or resolved. Changes in the Company's business, tax laws or laws, and developments in current and future tax audits, could significantly impact the amounts provided for income taxes in the Company's results of operations, financial position, or cash flows. Deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to tax benefit carry-forwards and to differences between the financial statement amounts of assets and liabilities and their respective tax basis. The Company regularly reviews its deferred tax assets for recoverability and establishes a valuation allowance if it is more likely than not that assets will not be realized. To make this assessment, the Company takes into account predictions of the amount and category of taxable income from various sources and all available positive and negative evidence about these possible sources of taxable potential effect of negative and positive evidence is commensurate with the extent to which the strength of the evidence can be objectively verified. The Company applies a two-step approach to determining the financial statement recognition and measurement of uncertain tax positions. The Company only recognizes an income tax expense or benefit with respect to uncertain tax positions in its financial statements that the Company judges is more likely than not to be sustained solely on its technical merits in a tax audit, including resolution of any related appeals or litigation processes. To make this judgment, the Company must interpret complex and sometimes ambiguous tax laws, regulations and administrative practices. If an income tax position meets the more likely than not recognition threshold, then the Company must measure the amount of the tax benefit to be recognized by determining the largest amount of tax benefit that has a greater than a 50% likelihood of being realized upon effective settlement with a taxing authority that has full knowledge of all of the relevant facts. It is inherently difficult and subjective to estimate such amounts, as this requires the Company to determine the probability of various possible settlement outcomes. To determine if a tax position is effectively settled after a tax examination has been completed, the Company must also estimate the likelihood that another taxing authority could review the respective tax position. The Company must also determine when it is reasonably possible that the amount of unrecognized tax benefits will significantly increase or decrease in the 12 months after each fiscal year-end. These judgments are difficult because a taxing authority may change its behavior as a result of the Company's disclosures in its financial statements. The Company must reevaluate its income tax positions on a quarterly basis to consider factors such as changes in facts or circumstances, changes in tax law, effectively settled issues under audit, and new audit activity. Such a change in recognition or measurement would result in recognition of a tax benefit or an additional charge to the tax provision. The Company's policy is to recognize interest and penalties related to unrecognized tax benefits as a component of the provision for income taxes.
Comprehensive income (loss)	Comprehensive Income (Loss) Other comprehensive income (loss) consists of unrealized gains (losses) on available-for-sale investments, net of tax, and derivative financial instruments including our hedging instruments designated as cash flow hedges which are not included in the Company’s net income. Total comprehensive income includes net income and other comprehensive income (loss) and is included in the consolidated statements of comprehensive income.
Foreign currency translation and transactions	Foreign Currency Transactions The Company’s operations are conducted in various countries around the world and the financial statements of its foreign subsidiaries are reported in the U.S. dollar as their respective functional currency. Monetary assets and liabilities denominated in foreign currencies have been re-measured into U.S. dollars using the exchange rates in effect at the balance sheet date, and income and expenses are re-measured at average exchange rates during the period. Foreign currency re-measurement gains and losses and foreign currency transaction gains and losses are recognized in other income (expense), net. The Company recorded total foreign currency transaction losses of $0.6 million , $0.4 million and $0.8 million during 2018 , 2017 and 2016 , respectively.
Fair value measurement	Fair Value Measurements Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. For certain of the Company’s financial instruments, including certain cash equivalents, accounts receivable, accounts payable, and other current liabilities, the carrying amounts approximate their fair value due to the relatively short maturity of these balances. The Company measures and reports certain cash equivalents, investments and derivative foreign currency forward contracts at fair value in accordance with the provisions of the authoritative accounting guidance that addresses fair value measurements. This guidance establishes a hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the most observable inputs be used when available. The hierarchy is broken down into three levels based on the reliability of inputs as follows: Level 1 —Valuations based on quoted prices in active markets for identical assets or liabilities. Level 2 —Valuations based on other than quoted prices in active markets for identical assets and liabilities, quoted prices for identical or similar assets or liabilities in inactive markets, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3— Valuations based on inputs that are generally unobservable and typically reflect management’s estimates of assumptions that market participants would use in pricing the asset or liability. The Company's financial instruments consist of assets measured using Level 1 and 2 inputs. Level 1 assets include a highly liquid money market fund, which is valued using unadjusted quoted prices that are available in an active market for an identical asset. Level 2 assets include fixed-income U.S. government agency securities, commercial paper, corporate bonds, asset-backed securities and derivative financial instruments consisting of foreign currency forward contracts. The securities, bonds and commercial paper are valued using prices from independent pricing services based on quoted prices in active markets for similar instruments or on industry models using data inputs such as interest rates and prices that can be directly observed or corroborated in active markets. The foreign currency forward contracts are valued using observable inputs , including currency spot rates, forward points as well as interest rates and credit rates for discounting . See Note 2 for more information regarding the fair value measurement of the Company's financial instruments.
Net income per share attributable to common stockholders	Net Income Per Share Basic net income per share is computed by dividing net income by the weighted-average number of common shares outstanding during the period. All participating securities are excluded from basic weighted average common shares outstanding. In computing diluted net income per share, undistributed earnings are reallocated to reflect the potential impact of dilutive securities. Diluted net income per share is computed by dividing net income by the weighted-average number of shares of common stock outstanding during the period, adjusted for the effects of potentially dilutive common shares, which are comprised of outstanding stock options . The dilutive potential common shares are computed using the treasury stock method or the as-if converted method, as applicable. The effects of outstanding stock options are excluded from the computation of diluted net income per common share in periods in which the effect would be anti-dilutive.
Recent accounting pronouncements	Recently Adopted Accounting Pronouncements The Company adopted Accounting Standards Codification ("ASC") 606 Revenue from Contracts with Customers with a date of initial application of January 1, 2018. The Company adopted ASC 606 using the modified retrospective method and recognized the cumulative effect of adoption as an adjustment to the opening balance of equity at January 1, 2018. Therefore, the comparative information from the prior period has not been adjusted and continues to be reported under ASC 605. The impact of adopting ASC 606 was related to the deferral of sales commission costs for new business and when customers increase their renewal orders (“upsells”). The Company previously expensed sales commissions as incurred. Under ASC 606, sales commissions cost related to new business and upsells are recorded as an asset. The Company amortizes the capitalized commission cost as a selling expense on a straight-line basis over a period of five years. Five years represents the estimated life of the customer relationship taking into account factors such as peer estimates of technology lives and customer lives as well as the Company's own historical data. Applying the practical expedient in ASC 340-40-25-4, the Company expenses commissions related to its contract renewals. The current and noncurrent portions of deferred commissions are included in prepaid expenses and other current assets, and other noncurrent assets, respectively, in its consolidated balance sheets. On January 1, 2018, the Company recorded an increase to retained earnings of $2.7 million , which was the net cumulative impact associated with the capitalization of sales commissions. Additionally, the Company recorded a corresponding commission asset balance of $3.5 million and a related deferred tax liability of $0.8 million . There was no impact to the Company's revenues as a result of adopting ASC 606. See Note 4, “Revenue from Contracts with Customers”, for additional information regarding the impact on the Company's consolidated financial statements. In January 2016, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities, which impacts certain aspects of recognition, measurement, presentation and disclosure of financial instruments. The ASU impacts the accounting for equity investments, financial liabilities under the fair value option, and the presentation and disclosure requirements for financial instruments. The Company adopted this ASU in its first quarter of 2018. The adoption of this ASU did not have a material impact on the Company's consolidated financial statements. In August 2016, the FASB issued ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments (a consensus of the Emerging Issues Task Force), to provide guidance on the presentation of certain cash receipts and cash payments in the statement of cash flows in order to reduce diversity in existing practice. The Company adopted this ASU in its first quarter of 2018. The adoption of this ASU did not have a material impact on the Company's consolidated financial statements. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash. The update provides guidance on the presentation of restricted cash or restricted cash equivalents in the statement of cash flows. The Company adopted this ASU retrospectively in its first quarter of 2018. The Company reclassified restricted cash of $1.2 million for each of the three years ended December 31, 2018, 2017 and 2016, in the consolidated statements of cash flows. In January 2017, the FASB issued ASU 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business, which revises the definition of a business and provides new guidance in evaluating when a set of transferred assets and activities is a business. The Company adopted this ASU prospectively in its first quarter of 2018. The adoption of this ASU did not have a material impact on the Company's consolidated financial statements. In August 2017, the FASB issued ASU 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities (Topic 815). This standard expands component and fair value hedging, specifies the presentation of the effects of hedging instruments, and eliminates the separate measurement and presentation of hedge ineffectiveness. The Company adopted ASU 2017-12 in the fourth quarter of 2018 and has concluded that the adoption had no impact on its consolidated financial statements. In February 2018, the FASB issued ASU 2018-02, Income Statement—Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income (AOCI). This ASU eliminates the stranded tax effects in other comprehensive income resulting from the Tax Cuts and Jobs Act (the "2017 Tax Act”). Because the amendments only relate to the reclassification of the income tax effects of the 2017 Tax Act, the underlying guidance that requires that the effect of a change in tax laws or rates be included in income from continuing operations is not affected. ASU 2018-02 is effective for the Company beginning in the first quarter of fiscal 2019 and early adoption is permitted. The Company adopted ASU 2018-02 in the fourth quarter of 2018 and has concluded that the adoption had no impact on its consolidated financial statements. Recently Issued Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which requires lessees to recognize all leases, including operating leases, on the balance sheet as a lease asset and lease liability, unless the lease is a short-term lease. ASU 2016-02 also requires additional disclosures regarding leasing arrangements. ASU 2016-02 is effective for the Company beginning in the first quarter of fiscal 2019 and early adoption is permitted. In July 2018, the FASB issued ASU 2018-11, Targeted Improvements - Leases (Topic 842). This update provides an optional transition method that allows entities to elect to apply the standard prospectively at its effective date, versus recasting the prior periods presented. In December 2018, the FASB issued ASU 2018-20, Narrow-Scope Improvements for Lessors - Leases (Topic 842). This update permits lessors, as an accounting policy election, to not evaluate whether certain sales taxes and other similar taxes are lessor costs or lessee costs. Instead, those lessors will account for those costs as if they are lessee costs. Pursuant to the leasing criteria, most of the Company's leased space and equipment leases will be required to be accounted for as right-of-use assets on the balance sheet with offsetting financing obligations. In the statement of operations, what was formerly rent expense for operating leases will be lease expense; and finance leases will be bifurcated into amortization of right-of-use assets and interest on lease liabilities. The Company plans to adopt the ASU utilizing the current period adjustment method on January 1, 2019 and to record approximately $37.6 million right-of-use assets and a $41.6 million lease liability on its consolidated balance sheet. The amount of the Company's deferred rent as of December 31, 2018 of $4.0 million will be removed upon adoption. In January 2017, the FASB issued ASU 2017-04, Simplifying the Test for Goodwill Impairment (Topic 350). This standard eliminates Step 2 from the goodwill impairment test, instead requiring an entity to recognize a goodwill impairment charge for the amount by which the goodwill carrying amount exceeds the reporting unit’s fair value. This ASU is effective for interim and annual goodwill impairment tests in fiscal years beginning after December 15, 2019 with early adoption permitted. This ASU must be applied on a prospective basis. The adoption of this ASU is not expected to have a material impact on the Company's consolidated financial statements. In June 2018, the FASB issued ASU 2018-07, Compensation - Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting. This ASU expands the scope of Topic 718 to include share-based payment transactions for acquiring goods and services from nonemployees. ASU 2018-07 is effective for the Company beginning in the first quarter of fiscal 2019 and early adoption is permitted. The Company is currently evaluating the impact of this ASU on its consolidated financial statements. In August 2018, the FASB issued ASU 2018-15, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. This ASU aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs related to internal-use software. ASU 2018-15 is effective for the Company beginning in the first quarter of fiscal 2020 and early adoption is permitted. The Company is currently evaluating the impact of this ASU on its consolidated financial statements.

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Schedule of Cash and Cash Equivalents, Available-for-sale Securities Reconciliation	The Company's cash and cash equivalents, short-term investments, and long-term investments consist of the following: December 31, 2018 Amortized Cost Unrealized Gains Unrealized Losses Fair Value (in thousands) Cash and cash equivalents: Cash $ 40,913 $ — $ — $ 40,913 Money market funds 113 — — 113 Total 41,026 — — 41,026 Short-term marketable securities : Commercial paper 3,237 — — 3,237 Corporate bonds 30,906 — (84 ) 30,822 Asset-backed securities 10,447 — (15 ) 10,432 U.S. government agencies 203,734 9 (94 ) 203,649 Total 248,324 9 (193 ) 248,140 Long-term marketable securities : Asset-backed securities 22,945 10 (28 ) 22,927 U.S. government agencies 18,804 — (53 ) 18,751 Corporate bonds 35,322 3 (293 ) 35,032 Total 77,071 13 (374 ) 76,710 Total $ 366,421 $ 22 $ (567 ) $ 365,876 December 31, 2017 Amortized Cost Unrealized Gains Unrealized Losses Fair Value (in thousands) Cash and cash equivalents: Cash $ 86,500 $ — $ — $ 86,500 Money market funds 91 — — 91 Total 86,591 — — 86,591 Short-term investments: Commercial paper 12,623 — (3 ) 12,620 Corporate bonds 38,425 1 (64 ) 38,362 U.S. government agencies 151,058 — (217 ) 150,841 Total 202,106 1 (284 ) 201,823 Long-term investments: Asset-backed securities 4,998 — (12 ) 4,986 U.S. government agencies 24,269 — (54 ) 24,215 Corporate bonds 38,198 — (175 ) 38,023 Total 67,465 — (241 ) 67,224 Total $ 356,162 $ 1 $ (525 ) $ 355,638
Schedule of Assets Measured on Recurring Basis	The following table sets forth by level within the fair value hierarchy the fair value of the Company's available-for-sale securities measured on a recurring basis, excluding cash and money market funds: December 31, 2018 Level 1 Level 2 Level 3 Fair Value (in thousands) Commercial paper $ — $ 3,237 $ — $ 3,237 U.S. government agencies — 222,400 — 222,400 Corporate bonds — 65,854 — 65,854 Asset-backed securities — 33,359 — 33,359 Total $ — $ 324,850 $ — $ 324,850 December 31, 2017 Level 1 Level 2 Level 3 Fair Value (in thousands) Commercial paper $ — $ 12,620 $ — $ 12,620 U.S. government agencies — 175,056 — 175,056 Corporate bonds — 76,385 — 76,385 Asset-backed securities — 4,986 — 4,986 Total $ — $ 269,047 $ — $ 269,047
Schedule of Investments Classified by Contractual Maturity	The following summarizes the fair value of securities classified as available-for-sale by contractual maturity: December 31, 2018 Mature within One Year After One Year through Two Years Over Two Years Fair Value (in thousands) Commercial paper $ 3,237 $ — $ — $ 3,237 U.S. government agencies 203,649 18,751 — 222,400 Corporate bonds 30,822 33,531 1,501 65,854 Asset-backed securities 29,026 4,333 — 33,359 Total $ 266,734 $ 56,615 $ 1,501 $ 324,850

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Property and equipment	Property and equipment consist of the following: December 31, 2018 2017 (in thousands) Computer equipment $ 93,530 $ 77,883 Computer software 26,030 20,447 Scanner appliances 15,356 14,325 Furniture, fixtures and equipment 5,814 5,075 Equipment under capital lease 3,503 — Leasehold improvements 16,439 16,067 Total property and equipment 160,672 133,797 Less: accumulated depreciation and amortization (99,230 ) (75,240 ) Property and equipment, net $ 61,442 $ 58,557

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Commission asset balances	Capitalized costs to obtain contracts, current and noncurrent are as follows (in thousands): December 31, 2018 January 1, 2018 Commission asset, current $ 1,480 $ 704 Commission asset, noncurrent $ 4,692 $ 2,819
Contract liabilities	Contract liabilities (deferred revenue) balances are as follows (in thousands): December 31, 2018 ASC 606 Operating Leases Total Deferred revenue, current $ 152,204 $ 12,420 $ 164,624 Deferred revenue, noncurrent 18,286 2,137 20,423 Total $ 170,490 $ 14,557 $ 185,047 January 1, 2018 ASC 606 Operating Leases Total Deferred revenue, current $ 130,579 $ 12,607 $ 143,186 Deferred revenue, noncurrent 15,419 1,717 17,136 Total $ 145,998 $ 14,324 $ 160,322
Accounts receivable, net	Accounts receivable, net, consists of the following (in thousands): December 31, 2018 January 1, 2018 ASC 606 receivables $ 71,387 $ 60,984 Operating lease receivables 5,121 4,244 Less: allowance for doubtful accounts (683 ) (816 ) Total accounts receivable, net $ 75,825 $ 64,412
Expected revenue from contracts	The following table sets forth the expected revenue from all remaining performance obligations as of December 31, 2018 (in thousands): ASC 606 Expected Revenue Operating Lease Expected Revenue Total Expected Revenue 2019 $ 46,682 $ 5,067 $ 51,749 2020 24,608 2,194 26,802 2021 10,730 1,071 11,801 2022 1,111 39 1,150 2023 348 9 357 2024 and thereafter 20 — 20 Total $ 83,499 $ 8,380 $ 91,879
Revenue by sales channel	Revenues by sales channel are as follows (in thousands): Year Ended December 31, 2018 ASC 606 Revenue Operating Lease Revenue Total Revenue Direct $ 148,310 $ 15,774 $ 164,084 Partner 106,816 7,989 114,805 Total $ 255,126 $ 23,763 $ 278,889

Business Combination (Tables)

Business Combination (Tables)	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Schedule of Business Acquisitions, by Acquisition [Table Text Block]	The allocation of the consideration for business combinations completed in 2018 is summarized as follows (in thousands): Acquiree Purchase Consideration Net Tangible Assets Acquired/ (liabilities assumed) Purchased Intangible Assets Goodwill Deferred Tax Liability 1Mobility $ 4,000 $ — $ 3,700 $ 300 $ — Layered Insight $ 13,434 $ 80 $ 9,600 $ 5,376 $ (1,622 ) The allocation of the consideration for business combinations completed in the year of 2017 is summarized as follows (in thousands): Acquiree Purchase Consideration Net Tangible Assets Acquired/ (liabilities assumed) Purchased Intangible Assets Goodwill Nevis $ 5,753 $ 14 $ 5,156 $ 583 NetWatcher 7,729 80 7,000 649 Total $ 13,482 $ 94 $ 12,156 $ 1,232

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets, Net (Tables)	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Carrying value of intangible assets	The carrying values of intangible assets as of December 31, 2018 are as follows (in thousands): December 31, 2018 Weighted Average Lives Weighted Remaining Average Lives Cost Accumulated Amortization Net Book Value Developed technology 5 years 4 years $ 25,456 $ (4,085 ) $ 21,371 Patent licenses 14 years 6 years 1,387 (822 ) 565 Total intangibles subject to amortization $ 26,843 $ (4,907 ) 21,936 Intangible assets not subject to amortization 40 Total intangible assets, net $ 21,976
Intangible assets future periods amortization expense	As of December 31, 2018 , the Company expects amortization expense in future periods to be as follows (in thousands): 2019 $ 5,856 2020 5,856 2021 5,856 2022 4,202 2023 100 2024 and thereafter 66 Total expected future amortization expense $ 21,936

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments for Operating Leases	The following are the minimum annual lease payments due under operating leases at December 31, 2018 (in thousands): 2019 8,173 2020 7,284 2021 6,046 2022 4,538 2023 4,298 2024 and thereafter 19,299 Total minimum lease payments $ 49,638

Employee Stock and Benefit Pl_2

Employee Stock and Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2018
Share-based Compensation [Abstract]
Schedule of shares reserved for future issuance	The Company had reserved shares of common stock for future issuance as of December 31, 2018 as follows: Options and RSUs outstanding under equity incentive plans 2000 Equity Incentive Plan 244,652 2012 Equity Incentive Plan 4,477,717 Shares available for future grants under an equity incentive plan 2012 Equity Incentive Plan 3,817,097 Total shares reserved for future issuance 8,539,466
Stock-based employee compensation	Stock-based compensation included in the consolidated statements of operations is as follows: Year Ended December 31, 2018 2017 2016 (in thousands) Cost of revenues $ 2,489 $ 2,159 $ 1,858 Research and development 7,961 5,944 5,678 Sales and marketing 4,650 4,755 4,870 General and administrative 14,990 14,103 7,743 Total stock-based employee compensation $ 30,090 $ 26,961 $ 20,149
Fair value assumptions of options granted to employees	The fair value of each option granted to employees is estimated on the date of grant using the Black-Scholes-Merton option-pricing model based on the following assumptions: Year Ended December 31, 2018 2017 2016 Expected term (in years) 4.5 to 5.0 5.1 to 5.5 5.0 to 5.9 Volatility 45% to 47% 47% to 49% 45% to 49% Risk-free interest rate 2.5% to 3.0% 1.8% to 2.0% 1.1% to 1.3% Dividend yield — — —
Stock option activity	A summary of the Company’s stock option activity is as follows: Outstanding Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Life (Years) Aggregate Intrinsic Value (in thousands) Balance as of December 31, 2015 7,579,058 $ 16.88 5.9 $ 131,345 Granted 2,120,633 $ 26.64 Exercised (1,399,157 ) $ 10.83 Canceled (772,854 ) $ 31.57 Balance as of December 31, 2016 7,527,680 $ 19.25 6.0 $ 101,717 Granted 408,225 $ 40.82 Exercised (2,997,095 ) $ 11.05 Canceled (442,919 ) $ 33.29 Balance as of December 31, 2017 4,495,891 $ 25.29 6.6 $ 153,129 Granted 366,786 $ 79.79 Exercised (1,183,235 ) $ 20.33 Canceled (250,133 ) $ 39.61 Balance as of December 31, 2018 3,429,309 $ 31.79 6.4 $ 149,935 Vested and expected to vest - December 31, 2018 3,230,498 $ 30.27 6.2 $ 145,521 Exercisable - December 31, 2018 2,459,936 $ 25.27 5.7 $ 121,696
Schedule of exercise price range, outstanding and vested	The following table summarizes the outstanding and vested stock options at December 31, 2018 : Outstanding Exercisable Exercise Price Number of Weighted Weighted Number of Weighted $2.80 - $12.68 376,405 $ 8.58 3.1 376,405 $ 8.58 $13.50 - $25.17 474,527 $ 21.70 5.4 412,956 $ 21.18 $25.56 - $25.56 886,676 $ 25.56 7.3 587,978 $ 25.56 $26.86 - $26.86 427,997 $ 26.86 5.1 427,997 $ 26.86 $30.58 - $34.97 372,331 $ 31.78 6.2 307,743 $ 31.54 $36.25 - $40.15 391,568 $ 37.78 7.2 225,200 $ 37.53 $40.68 - $59.95 213,744 $ 49.97 7.6 121,460 $ 45.16 $76.21 - $76.21 101,125 $ 76.21 9.8 — $ — $78.85 - $78.85 78,550 $ 78.85 9.3 93 $ 78.85 $95.10 - $95.10 106,386 $ 95.10 9.5 104 $ 95.10 3,429,309 $ 31.79 6.4 2,459,936 $ 25.27
Summary of the Company’s RSUs and RSAs activity	A summary of the Company’s RSU activity is as follows: Number of Shares Weighted-Average Grant Date Fair Value Per Share Balance as of December 31, 2015 47,500 $ 37.28 Granted 681,350 $ 28.52 Vested (39,998 ) $ 27.49 Cancelled (101,519 ) $ 31.12 Balance as of December 31, 2016 587,333 $ 28.85 Granted 1,326,849 $ 42.69 Vested (368,367 ) $ 33.52 Cancelled (135,227 ) $ 32.04 Balance as of December 31, 2017 1,410,588 $ 40.34 Granted 548,245 $ 75.44 Vested (525,375 ) $ 39.87 Cancelled (206,575 ) $ 43.43 Balance as of December 31, 2018 1,226,883 $ 55.71 Outstanding and expected to vest - December 31, 2018 898,637 $ 54.67

Other Income (Expense), Net (Ta

Other Income (Expense), Net (Tables)	12 Months Ended
	Dec. 31, 2018
Other Income and Expenses [Abstract]
Schedule of Other Nonoperating Income (Expense)	Other expense, net consists of the following: Year Ended December 31, 2018 2017 2016 (in thousands) Foreign exchange losses $ (577 ) $ (355 ) $ (770 ) Other expense (224 ) (181 ) (202 ) Other expense, net $ (801 ) $ (536 ) $ (972 )

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Schedule of Geographical Breakdown of Income (Loss) Before Provision for (Benefit From) Income Taxes	The Company’s geographical breakdown of income before income taxes is as follows: Year Ended December 31, 2018 2017 2016 (in thousands) Domestic $ 50,010 $ 34,914 $ 28,982 Foreign 5,458 4,464 1,447 Income before income taxes $ 55,468 $ 39,378 $ 30,429
Schedule of Provision for (Benefit From) Income Taxes	The provision for (benefit from) income taxes consists of the following: Year Ended December 31, 2018 2017 2016 (in thousands) Current Federal $ (90 ) $ 22 $ 8,334 State 62 23 1,125 Foreign 1,988 1,471 963 Total current provision 1,960 1,516 10,422 Deferred Federal (3,449 ) (1,650 ) 611 State 21 (996 ) 126 Foreign (368 ) 68 46 Total deferred (benefit) provision (3,796 ) (2,578 ) 783 Total (benefit from) provision for income taxes $ (1,836 ) $ (1,062 ) $ 11,205
Schedule of Effective Income Tax Rate Reconciliation	The reconciliation of the statutory federal income tax rate to the Company’s effective tax rate is as follows: Year Ended December 31, 2018 2017 2016 Federal statutory rate 21.0 % 35.0 % 35.0 % State taxes (1.9 ) (2.1 ) 2.1 Stock-based compensation (20.4 ) (58.1 ) 2.4 Foreign source income (0.2 ) (0.2 ) 0.9 Change in valuation allowance 4.4 2.8 1.3 Federal rate adjustment (due to 2017 Tax Act) — 26.4 — Federal and state research and development credit (6.7 ) (5.3 ) (3.6 ) Other 0.5 (1.2 ) (1.3 ) (Benefit from) provision for income taxes (3.3 )% (2.7 )% 36.8 %
Schedule of Deferred Tax Assets and Liabilities	December 31, 2018 2017 (in thousands) Deferred tax assets Net operating loss carryforwards $ 11,250 $ 8,947 Research and development credit carryforwards 16,901 11,493 Foreign tax credit carryforwards 2,209 1,149 Accrued liabilities 2,723 1,470 Deferred revenues 4,200 3,416 Intangible assets — 405 Stock-based compensation 6,975 7,135 Other 174 196 Gross deferred tax assets 44,432 34,211 Valuation allowance (9,100 ) (5,773 ) Net deferred tax assets 35,332 28,438 Deferred tax liabilities Fixed assets (8,161 ) (3,372 ) Intangible assets (784 ) — Total deferred tax liabilities (8,945 ) (3,372 ) Net deferred tax assets $ 26,387 $ 25,066
Schedule of Unrecognized Tax Benefits	Year Ended December 31, 2018 2017 2016 Unrecognized tax benefits beginning balance $ 5,112 $ 4,071 $ 3,506 Gross increase for tax positions of prior years 279 66 2 Gross decrease for tax positions of prior years (227 ) — (15 ) Gross increase for tax positions of current year 1,399 1,101 659 Lapse of statute of limitations (157 ) (126 ) (81 ) Total unrecognized tax benefits $ 6,406 $ 5,112 $ 4,071

Segment Information and Infor_2

Segment Information and Information about Geographic Area (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Revenues and property and equipment, net, by geographic area	Revenues by geographic area, based on the location of the customer, are as follows: Year Ended December 31, 2018 2017 2016 (in thousands) United States $ 185,887 $ 162,681 $ 139,743 Foreign 93,002 68,147 58,182 Total revenues $ 278,889 $ 230,828 $ 197,925 Property and equipment, net, by geographic area, are as follows: December 31, 2018 2017 (in thousands) United States $ 59,222 $ 50,785 Foreign 2,220 7,772 Total property and equipment, net $ 61,442 $ 58,557

Net Income Per Share Attribut_2

Net Income Per Share Attributable to Common Stockholders (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The computations for basic and diluted net income per share are as follows: Year Ended December 31, 2018 2017 2016 (in thousands, except per share data) Numerator: Net income - basic and diluted $ 57,304 $ 40,440 $ 19,224 Denominator: Weighted-average shares used in computing net income per share - basic 38,876 37,443 35,247 Effect of potentially dilutive securities: Common stock options 2,401 2,262 3,052 RSUs 620 366 70 Weighted-average shares used in computing net income per share - diluted 41,897 40,071 38,369 Net income per share: Basic $ 1.47 $ 1.08 $ 0.55 Diluted $ 1.37 $ 1.01 $ 0.50
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	otentially dilutive securities not included in the calculation of diluted net income per share because doing so would be anti-dilutive are as follows: Year Ended December 31, 2018 2017 2016 (in thousands) Common stock options 177 742 3,241 RSUs 22 71 24

Quarterly Financial Informati_2

Quarterly Financial Information (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	Three Months Ended Mar. 31, 2017 Jun. 30, 2017 Sep. 30, 2017 Dec. 31, 2017 Mar. 31, 2018 Jun. 30, 2018 Sep. 30, 2018 Dec. 31, 2018 (unaudited) (in thousands, except per share data) Revenues $ 53,121 $ 55,302 $ 59,490 $ 62,915 $ 64,878 $ 68,153 $ 71,658 $ 74,200 Income from operations 7,656 9,009 10,849 9,729 8,406 10,895 18,117 12,943 Other income, net 453 360 671 652 1,245 884 1,116 1,862 Income before income taxes 8,109 9,369 11,520 10,381 9,651 11,779 19,233 14,805 Net income 21,930 7,202 8,452 2,857 9,142 10,293 23,469 14,400 Net income per share: Basic $ 0.60 $ 0.19 $ 0.22 $ 0.07 $ 0.24 $ 0.26 $ 0.60 $ 0.37 Diluted $ 0.56 $ 0.18 $ 0.21 $ 0.07 $ 0.22 $ 0.24 $ 0.56 $ 0.35

The Company and Summary of Si_3

The Company and Summary of Significant Accounting Policies (Details) $ in Thousands, € in Millions, £ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Jan. 01, 2019USD ($)	Dec. 31, 2018GBP (£)	Dec. 31, 2018EUR (€)	Dec. 31, 2018USD ($)	Sep. 30, 2018GBP (£)customer	Sep. 30, 2018EUR (€)customer	Sep. 30, 2018USD ($)customer	Jan. 01, 2018USD ($)	Jan. 01, 2017USD ($)
The company and qualitative disclosure about market risk [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net			$ 543	$ (1,665)	$ 554
Retained earnings				39,924						$ 27,964
Capitalized Computer Software, Gross				400	0					1,300
Capitalized Computer Software, Unamortized				300						1,200
Long-term investments				0						2,500
General and administrative			39,049	35,334	29,114
Cost of revenues			66,185	51,580	43,128
Research and development			53,255	42,816	36,591
Sales and marketing			70,039	63,855	58,985
Software Development Costs
Capitalized software development costs					0
Cost of intangible assets				15,455									$ 26,843
Accumulated amortization of intangible assets				3,094									$ 4,907
Derivative Financial Instruments
Derivative, notional amount											£ 4.8	€ 7
Other foreign currency transaction gains (losses)			(1,120)	1,310	(1,324)
Total foreign exchange loss, net			(577)	(355)	(770)
Advertising Expenses
Advertising expense		$ 482	87			$ 124
Income Taxes
Tax Cuts and Jobs Act of 2017, Provisional income tax expense (benefit)	$ 10,400
Noncurrent deferred tax assets				25,066						26,387
Cumulative effect adjustment														$ 2,711
Provision for (benefit from) income taxes			$ (1,836)	(1,062)	$ 11,205
Restricted cash				1,200						$ 1,200
Minimum
Property Equipment, Net
Property, plant and equipment, useful life	3 years
Goodwill and Intangible Assets
Finite-lived intangible asset, useful life	3 years
Maximum
Property Equipment, Net
Property, plant and equipment, useful life	5 years
Goodwill and Intangible Assets
Finite-lived intangible asset, useful life	14 years
Scanner appliances
Property Equipment, Net
Property, plant and equipment, useful life	3 years
Foreign Exchange Contract [Member]
Derivative Financial Instruments
Derivative, notional amount								£ 4.1	€ 12.9
Forward contracts
Derivative Financial Instruments
Derivative, notional amount											£ 6.3	€ 16
Foreign currency contract, asset, fair value disclosure				0
Software and software development costs
Software Development Costs
Cost of intangible assets				$ 400
Customer concentration risk | Accounts receivable
Concentration of Credit Risk
Concentration risk, number of customers | customer											0	0	0
Accounting Standards Update 2016-09
Income Taxes
Cumulative effect adjustment															$ 7,745
Accounting Standards Update 2016-09 | Retained earnings
Income Taxes
Cumulative effect adjustment															$ 7,745
Subsequent Event | Operating Leases | Scenario, Forecast
Income Taxes
Right of use asset							$ 37,600
Operating lease, liability							41,600
Deferred rent							$ 4,000

Fair Value of Financial Instr_3

Fair Value of Financial Instruments (Cash and Cash Equivalents, Available-for-sale Securities, Restricted Cash Reconciliation) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	$ (366,421)	$ (356,162)
Unrealized Gains	22	1
Unrealized Losses	(567)	(525)
Fair value	365,876	355,638
Cash and Cash Equivalents
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	(41,026)	(86,591)
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair value	41,026	86,591
Cash and Cash Equivalents | Cash
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	(40,913)	(86,500)
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair value	40,913	86,500
Cash and Cash Equivalents | Money market funds
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	(113)	(91)
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair value	113	91
Short-term Investments
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	(248,324)	(202,106)
Unrealized Gains	9	1
Unrealized Losses	(193)	(284)
Fair value	248,140	201,823
Short-term Investments | U.S. government agencies
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	(203,734)	(151,058)
Unrealized Gains	9	0
Unrealized Losses	(94)	(217)
Fair value	203,649	150,841
Short-term Investments | Commercial paper
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	(3,237)	(12,623)
Unrealized Gains	0	0
Unrealized Losses	0	(3)
Fair value	3,237	12,620
Short-term Investments | Corporate bonds
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	(30,906)	(38,425)
Unrealized Gains	0	1
Unrealized Losses	(84)	(64)
Fair value	30,822	38,362
Short-term Investments | Asset-backed securities
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	(10,447)
Unrealized Gains	0
Unrealized Losses	(15)
Fair value	10,432
Long-Term Investments
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	(77,071)	(67,465)
Unrealized Gains	13	0
Unrealized Losses	(374)	(241)
Fair value	76,710	67,224
Long-Term Investments | U.S. government agencies
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	(18,804)	(24,269)
Unrealized Gains	0	0
Unrealized Losses	(53)	(54)
Fair value	18,751	24,215
Long-Term Investments | Corporate bonds
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	(35,322)	(38,198)
Unrealized Gains	3	0
Unrealized Losses	(293)	(175)
Fair value	35,032	38,023
Long-Term Investments | Asset-backed securities
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	(22,945)	(4,998)
Unrealized Gains	10	0
Unrealized Losses	(28)	(12)
Fair value	$ 22,927	$ 4,986

Fair Value of Financial Instr_4

Fair Value of Financial Instruments (Fair Value Hierarchy) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	$ 324,850
Recurring Basis | Fair Value
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	324,850	$ 269,047
Level 1 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	0	0
Level 2 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	324,850	269,047
Level 3 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	0	0
Commercial paper
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	3,237
Commercial paper | Recurring Basis | Fair Value
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	3,237	12,620
Commercial paper | Level 1 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	0	0
Commercial paper | Level 2 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	3,237	12,620
Commercial paper | Level 3 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	0	0
U.S. government agencies
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	222,400
U.S. government agencies | Recurring Basis | Fair Value
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	222,400	175,056
U.S. government agencies | Level 1 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	0	0
U.S. government agencies | Level 2 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	222,400	175,056
U.S. government agencies | Level 3 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	0	0
Corporate bonds
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	65,854
Corporate bonds | Recurring Basis | Fair Value
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	65,854	76,385
Corporate bonds | Level 1 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	0	0
Corporate bonds | Level 2 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	65,854	76,385
Corporate bonds | Level 3 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	0	0
Asset-backed securities
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	33,359
Asset-backed securities | Recurring Basis | Fair Value
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	33,359	4,986
Asset-backed securities | Level 1 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	0	0
Asset-backed securities | Level 2 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	33,359	4,986
Asset-backed securities | Level 3 | Recurring Basis
Assets, Fair Value Disclosure [Abstract]
Available-for-sale securities, fair value	$ 0	$ 0

Fair Value of Financial Instr_5

Fair Value of Financial Instruments (Contractual Maturity) (Details) $ in Thousands	Dec. 31, 2018USD ($)
Schedule of Available-for-sale Securities [Line Items]
Mature within One Year	$ 266,734
After One Year through Two Years	56,615
Over Two Years	1,501
Fair Value	324,850
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Mature within One Year	3,237
After One Year through Two Years	0
Over Two Years	0
Fair Value	3,237
U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Mature within One Year	203,649
After One Year through Two Years	18,751
Over Two Years	0
Fair Value	222,400
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Mature within One Year	30,822
After One Year through Two Years	33,531
Over Two Years	1,501
Fair Value	65,854
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Mature within One Year	29,026
After One Year through Two Years	4,333
Over Two Years	0
Fair Value	$ 33,359

Fair Value of Financial Instr_6

Fair Value of Financial Instruments (Narrative) (Details) $ in Thousands	Dec. 31, 2017USD ($)
Forward contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contract, asset, fair value disclosure	$ 0

Property and Equipment, Net (De

Property and Equipment, Net (Details) - USD ($) $ in Thousands	Nov. 20, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2018
Property, Plant and Equipment [Line Items]
Property and equipment			$ 133,797		$ 160,672
Less: accumulated depreciation and amortization			(75,240)		(99,230)
Property and equipment, net		$ 61,442	58,557		61,442
Depreciation and amortization expense		25,100	19,900	$ 16,600
Loss on disposal of office facilities	$ 200
Gross amount of abandoned costs	2,400
Accumulated depreciation on abandoned facility	$ 2,200
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment			77,883		93,530
Computer software
Property, Plant and Equipment [Line Items]
Property and equipment			20,447		26,030
Furniture, fixtures and equipment
Property, Plant and Equipment [Line Items]
Property and equipment			5,075		5,814
Equipment Under Capital Lease [Member]
Property, Plant and Equipment [Line Items]
Property and equipment			0		3,503
Scanner appliances
Property, Plant and Equipment [Line Items]
Property and equipment			14,325		15,356
Scanner appliances and other computer equipment subject to subscription
Property, Plant and Equipment [Line Items]
Property and equipment, net		7,900	6,800
Scanner appliances and other computer equipment not placed in service
Property, Plant and Equipment [Line Items]
Property and equipment		1,800	900
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment			16,067		$ 16,439
Other fixed assets not placed in service
Property, Plant and Equipment [Line Items]
Property and equipment		$ 3,700	$ 9,600

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Jan. 01, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings	$ 27,964	$ 39,924	$ 27,964	$ 39,924
Deferred tax liability	8,945		8,945		$ 3,372
Amortization of commissions assets			1,200
Revenue recognized	74,200	$ 62,915	278,889
Unbilled contracts	$ 91,879		91,879
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings						$ 2,711
Commission asset balance						3,500
Deferred tax liability						$ 800
Subscription Revenue
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue recognized			$ 141,300	$ 112,700

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Commission Asset Balances (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018
Revenue from Contract with Customer [Abstract]
Commission asset, current	$ 1,480	$ 704
Commission asset, noncurrent	$ 4,692	$ 2,819

Revenue from Contracts with C_5

Revenue from Contracts with Customers - Deferred Revenues (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Deferred Revenue Arrangement [Line Items]
Deferred revenue, current	$ 164,624	$ 143,186	$ 143,186
Deferred revenue, noncurrent	20,423	17,136	$ 17,136
Total	185,047	160,322
ASC 606
Deferred Revenue Arrangement [Line Items]
Deferred revenue, current	152,204	130,579
Deferred revenue, noncurrent	18,286	15,419
Total	170,490	145,998
Operating Leases
Deferred Revenue Arrangement [Line Items]
Deferred revenue, current	12,420	12,607
Deferred revenue, noncurrent	2,137	1,717
Total	$ 14,557	$ 14,324

Revenue from Contracts with C_6

Revenue from Contracts with Customers - Accounts Receivable, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
ASC 606 receivables	$ 71,387		$ 60,984
Operating lease receivables	5,121		4,244
Allowance for doubtful accounts receivable	(683)	$ (683)	(816)	$ (816)
Total accounts receivable, net	$ 75,825		$ 64,412	$ 64,412

Revenue from Contracts with C_7

Revenue from Contracts with Customers - Unbilled contracts (Details) $ in Thousands	Dec. 31, 2018USD ($)
Deferred Revenue Arrangement [Line Items]
Contracts expected to be billed remainder of year	$ 51,749
Unbilled Receivables, Expected To Be Billed In 2019	26,802
Unbilled Receivables, Expected To Be Billed In 2020	11,801
Unbilled Receivables, Expected To Be Billed In 2021	1,150
Unbilled Receivables, Expected To Be Billed In 2022	357
Unbilled Receivables, Expected To Be Billed Thereafter	20
Unbilled Receivables, Not Billable	91,879
ASC 606
Deferred Revenue Arrangement [Line Items]
Contracts expected to be billed remainder of year	46,682
Unbilled Receivables, Expected To Be Billed In 2019	24,608
Unbilled Receivables, Expected To Be Billed In 2020	10,730
Unbilled Receivables, Expected To Be Billed In 2021	1,111
Unbilled Receivables, Expected To Be Billed In 2022	348
Unbilled Receivables, Expected To Be Billed Thereafter	20
Unbilled Receivables, Not Billable	83,499
Operating Lease Expected Revenue
Deferred Revenue Arrangement [Line Items]
Contracts expected to be billed remainder of year	5,067
Unbilled Receivables, Expected To Be Billed In 2019	2,194
Unbilled Receivables, Expected To Be Billed In 2020	1,071
Unbilled Receivables, Expected To Be Billed In 2021	39
Unbilled Receivables, Expected To Be Billed In 2022	9
Unbilled Receivables, Expected To Be Billed Thereafter	0
Unbilled Receivables, Not Billable	$ 8,380

Revenue from Contracts with C_8

Revenue from Contracts with Customers - Revenue by sales channel (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 74,200	$ 62,915	$ 278,889
Direct
Disaggregation of Revenue [Line Items]
Revenues			164,084
Partner
Disaggregation of Revenue [Line Items]
Revenues			114,805
ASC 606
Disaggregation of Revenue [Line Items]
Revenues			255,126
ASC 606 | Direct
Disaggregation of Revenue [Line Items]
Revenues			148,310
ASC 606 | Partner
Disaggregation of Revenue [Line Items]
Revenues			106,816
Operating Lease Expected Revenue
Disaggregation of Revenue [Line Items]
Revenues			23,763
Operating Lease Expected Revenue | Direct
Disaggregation of Revenue [Line Items]
Revenues			15,774
Operating Lease Expected Revenue | Partner
Disaggregation of Revenue [Line Items]
Revenues			$ 7,989

Business Combination (Details)

Business Combination (Details) - USD ($) $ in Thousands	Jan. 10, 2019	Oct. 16, 2018	Apr. 01, 2018	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Purchased Intangible Assets						$ 12,156
Goodwill					$ 7,225	1,549
Total purchase price						13,482
Cash payment to acquire businesses				$ 12,500	13,633	12,482	$ 0
Estimated useful life of technology-based intangible assets				5 years
Layered Insight
Business Acquisition [Line Items]
Purchased Intangible Assets					9,600
Goodwill					5,376
Total purchase price		$ 13,400
Reserve fund		1,600
Business Combination, Additional Consideration		4,000
Business Combination, Earnout Milestone		1,500
Business Combination, Future Payments To Key Employees		$ 4,000
Estimated useful life of technology-based intangible assets		4 years
1Mobility
Business Acquisition [Line Items]
Purchased Intangible Assets					3,700
Goodwill					300
Total purchase price					4,000
Reserve fund					$ 600
Estimated useful life of technology-based intangible assets			4 years
Nevis
Business Acquisition [Line Items]
Purchased Intangible Assets						5,156
Goodwill						583
Total purchase price						5,753
NetWatcher
Business Acquisition [Line Items]
Purchased Intangible Assets						7,000
Goodwill						649
Total purchase price						$ 7,729
Reserve fund				$ 1,000
Future payments for continued employment, year 1				1 year
Future payments for continued employment, year 2				2 years
Subsequent Event
Business Acquisition [Line Items]
Payments For Asset Acquisitions, Payable In Future, Round 1	$ 200
Payments For Asset Acquisitions, Payable In Future, Round 2	600
Subsequent Event | Adya Assets Acquisition [Member]
Business Acquisition [Line Items]
Payments For Asset Acquisitions	$ 1,000

Business Combination - Schedule

Business Combination - Schedule of consideration allocation (Details) - USD ($) $ in Thousands	Oct. 16, 2018	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Purchase Consideration			$ 13,482
Net Tangible Assets Acquired/ (liabilities assumed)			94
Purchased Intangible Assets			12,156
Goodwill		$ 7,225	1,549
1Mobility
Business Acquisition [Line Items]
Purchase Consideration		4,000
Net Tangible Assets Acquired/ (liabilities assumed)		0
Purchased Intangible Assets		3,700
Goodwill		300
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities		0
Layered Insight
Business Acquisition [Line Items]
Purchase Consideration	$ 13,400
Net Tangible Assets Acquired/ (liabilities assumed)		80
Purchased Intangible Assets		9,600
Goodwill		5,376
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities		$ (1,622)
Nevis
Business Acquisition [Line Items]
Purchase Consideration			5,753
Net Tangible Assets Acquired/ (liabilities assumed)			14
Purchased Intangible Assets			5,156
Goodwill			583
NetWatcher
Business Acquisition [Line Items]
Purchase Consideration			7,729
Net Tangible Assets Acquired/ (liabilities assumed)			80
Purchased Intangible Assets			7,000
Goodwill			649
Nevis and NetWatcher
Business Acquisition [Line Items]
Goodwill			$ 1,232

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets, Net (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017
Schedule of Goodwill and Intangible Assets [Line Items]
Purchased Intangible Assets				$ 12,156
Cost	$ 26,843			15,455
Accumulated Amortization	(4,907)			(3,094)
Net Book Value	21,936			12,361
Intangible assets not subject to amortization	40			40
Total intangible assets, net	21,976		$ 21,976	12,401
Amortization of intangible assets	$ 3,700	$ 700
Goodwill			7,225	1,549
Existing technology
Schedule of Goodwill and Intangible Assets [Line Items]
Estimated Lives	5 years	5 years
Weighted Remaining Average Lives	4 years	5 years
Cost	$ 25,456			14,067
Accumulated Amortization	(4,085)			(2,371)
Net Book Value	$ 21,371			11,696
Patent license
Schedule of Goodwill and Intangible Assets [Line Items]
Estimated Lives	14 years	14 years
Weighted Remaining Average Lives	6 years	7 years
Cost	$ 1,387			1,388
Accumulated Amortization	(822)			(723)
Net Book Value	$ 565			$ 665
1Mobility
Schedule of Goodwill and Intangible Assets [Line Items]
Purchased Intangible Assets			3,700
Goodwill			300
Layered Insight
Schedule of Goodwill and Intangible Assets [Line Items]
Purchased Intangible Assets			9,600
Goodwill			$ 5,376

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets, Net (Future Amortization) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
2,017	$ 5,856
2,018	5,856
2,019	5,856
2,020	4,202
2,021	100
2021 and thereafter	66
Net Book Value	$ 21,936	$ 12,361

Commitments and Contingencies_2

Commitments and Contingencies (Future Minimum Lease Payments) (Details) $ in Thousands	Sep. 30, 2018USD ($)
Operating Leases
2,018	$ 8,173
2,019	7,284
2,021	6,046
2,022	4,538
Operating Leases, Future Minimum Payments, Due in Five Years	4,298
Thereafter	19,299
Total minimum lease payments	$ 49,638

Commitments and Contingencies_3

Commitments and Contingencies (Additional Information) (Details) - USD ($) $ in Thousands	Oct. 14, 2016	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2015	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Rent expense		$ 9,900	$ 9,600	$ 7,100
Deferred rent credit, noncurrent		10,800			$ 9,500
Operating Leased Assets [Line Items]
Total lease commitments		$ 49,638
Standby letters of credit for headquarters
Operating Leased Assets [Line Items]
Maximum borrowing capacity	$ 1,200
Lease agreement for headquarters
Operating Leased Assets [Line Items]
Lease term	10 years
Total lease commitments	$ 36,400

Employee Stock and Benefit Pl_3

Employee Stock and Benefit Plans (Common Stock and Preferred Stock) (Details) - $ / shares	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Oct. 03, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options and RSUs outstanding under equity incentive plans	3,429,309		4,495,891	7,527,680	7,579,058
Total shares reserved for future issuance	8,539,466
Preferred Stock
Preferred stock, shares authorized		20,000,000	20,000,000
Preferred stock, par value per share (in dollars per share)		$ 0.001	$ 0.001
Preferred stock, shares issued		0	0
Preferred stock, shares outstanding		0	0
Preferred Stock
Preferred Stock
Preferred stock, shares authorized						20,000,000
Preferred stock, par value per share (in dollars per share)						$ 0.001
2000 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options and RSUs outstanding under equity incentive plans	244,652
2012 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options and RSUs outstanding under equity incentive plans	4,477,717
Shares available for future grants under an equity incentive plan	3,817,097

Employee Stock and Benefit Pl_4

Employee Stock and Benefit Plans (Plan Information) (Details) - shares	Sep. 26, 2012	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
2012 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)				11,791,179
Shares available for future grants under an equity incentive plan			3,817,097
2012 Equity Incentive Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
2012 Equity Incentive Plan | Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years
Term of award	10 years
2000 Equity Incentive Plan | Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		4 years
Term of award		10 years
Number of shares available for issuance (in shares)		0
2000 Equity Incentive Plan | Stock Options | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award strike price as a percentage of market value		85.00%
Increase of Number of Shares Option | 2012 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity incentive plan annual increase (in shares)	3,050,000
Increase of Percentage of Shares Outstanding Option | 2012 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity incentive plan, annual increase, percent of shares outstanding	5.00%

Employee Stock and Benefit Pl_5

Employee Stock and Benefit Plans (Expense) (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based employee compensation			$ 30,090	$ 26,961	$ 20,149
Unrecognized employee compensation cost	$ 13,800
Unrecognized employee compensation cost, period for recognition	2 years 1 month 10 days
Non-employee share-based compensation expense	$ 400	$ 900				$ 700
Contributions by the Company to the 401(k) plan			1,200	1,100
Restricted Stock Units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Unrecognized employee compensation cost	$ 54,300
Unrecognized employee compensation cost, period for recognition	2 years 7 months 28 days
Cost of revenues
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based employee compensation			2,489	2,159	1,858
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based employee compensation			7,961	5,944	5,678
Sales and marketing
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based employee compensation			4,650	4,755	4,870
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based employee compensation			$ 14,990	$ 14,103	$ 7,743

Employee Stock and Benefit Pl_6

Employee Stock and Benefit Plans (Fair Value Assumptions, Stock Options) (Details) - Stock Options	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield			0.00%	0.00%	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	4 years 5 months 20 days	5 years 1 month				5 years
Volatility	45.00%	47.00%				45.00%
Risk-free interest rate	2.50%	1.80%				1.10%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	5 years	5 years 5 months 15 days				5 years 10 months 24 days
Volatility	47.00%	49.00%				49.00%
Risk-free interest rate	3.00%	2.00%				1.30%

Employee Stock and Benefit Pl_7

Employee Stock and Benefit Plans (Stock Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Outstanding Shares
Beginning balance (in shares)	4,495,891	7,527,680	7,579,058
Granted (in shares)	366,786	408,225	2,120,633
Exercised (in shares)	(1,183,235)	(2,997,095)	(1,399,157)
Canceled (in shares)	(250,133)	(442,919)	(772,854)
Ending balance (in shares)	3,429,309	4,495,891	7,527,680	7,579,058
Vested and Expected to vest (in shares)	3,230,498
Exercisable (in shares)	2,459,936
Weighted Average Exercise Price
Weighted average exercise price, beginning balance (in dollars per share)	$ 25.29	$ 19.25	$ 16.88
Weighted average exercise price, granted (in dollars per share)	79.79	40.82	26.64
Weighted average exercise price, exercised (in dollars per share)	20.33	11.05	10.83
Weighted average exercise price, canceled (in dollars per share)	39.61	33.29	31.57
Weighted average exercise price, ending balance (in dollars per share)	31.79	$ 25.29	$ 19.25	$ 16.88
Vested and Expected to vest, weighted average exercise price (in dollars per share)	30.27
Exercisable, Weighted average exercise price (in dollars per share)	$ 25.27
Weighted Average Remaining Contractual Life (Years)
Weighted average remaining contractual life	6 years 4 months 10 days	6 years 7 months 6 days	6 years	5 years 10 months 24 days
Vested and Expected to vest, weighted average remaining contractual life	6 years 2 months 2 days
Exercisable, weighted average remaining contractual life	5 years 7 months 25 days
Aggregate Intrinsic Value
Aggregate intrinsic value	$ 149,935	$ 153,129	$ 101,717	$ 131,345
Vested and Expected to vest, aggregate intrinsic value	145,521
Exercisable, aggregate intrinsic value	$ 121,696

Employee Stock and Benefit Pl_8

Employee Stock and Benefit Plans (Options Outstanding and Vested) (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2015
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of shares, outstanding			3,429,309
Weighted average exercise price per share, outstanding (in dollar per share)			$ 31.79
Weighted average remaining contractual life, outstanding			6 years 4 months 10 days
Number of shares, vested			2,459,936,000
Weighted average exercise price per share, vested (in dollar per share)			$ 25.27
Stock Options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Weighted average grant date fair value (in dollars per share)	$ 33.05	$ 18.03		$ 11.12
Aggregate grant date fair value	$ 12.1	$ 7.4		$ 23.6
Intrinsic value of options exercised	$ 71.7	$ 92.1		$ 25
$1.90 - $1.90
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollar per share)	$ 2.60
Exercise price range, upper limit (in dollar per share)	4.40
Number of shares, outstanding			376,405
Weighted average exercise price per share, outstanding (in dollar per share)			$ 8.58
Weighted average remaining contractual life, outstanding			3 years 26 days
Number of shares, vested			376,405,000
Weighted average exercise price per share, vested (in dollar per share)			$ 8.58
$2.10 - $2.80
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollar per share)	4.80
Exercise price range, upper limit (in dollar per share)	13.60
Number of shares, outstanding			474,527
Weighted average exercise price per share, outstanding (in dollar per share)			$ 21.70
Weighted average remaining contractual life, outstanding			5 years 4 months 7 days
Number of shares, vested			412,956,000
Weighted average exercise price per share, vested (in dollar per share)			$ 21.18
$3.80 - $3.80
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollar per share)	16.68
Exercise price range, upper limit (in dollar per share)	25.17
Number of shares, outstanding			886,676
Weighted average exercise price per share, outstanding (in dollar per share)			$ 25.56
Weighted average remaining contractual life, outstanding			7 years 3 months
Number of shares, vested			587,978,000
Weighted average exercise price per share, vested (in dollar per share)			$ 25.56
$4.10 - $12.68
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollar per share)	25.56
Exercise price range, upper limit (in dollar per share)	25.56
Number of shares, outstanding			427,997
Weighted average exercise price per share, outstanding (in dollar per share)			$ 26.86
Weighted average remaining contractual life, outstanding			5 years 1 month
Number of shares, vested			427,997,000
Weighted average exercise price per share, vested (in dollar per share)			$ 26.86
$13.50 - $25.17
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollar per share)	26.58
Exercise price range, upper limit (in dollar per share)	26.86
Number of shares, outstanding			372,331
Weighted average exercise price per share, outstanding (in dollar per share)			$ 31.78
Weighted average remaining contractual life, outstanding			6 years 2 months 6 days
Number of shares, vested			307,743,000
Weighted average exercise price per share, vested (in dollar per share)			$ 31.54
$25.56 - $25.56
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollar per share)	30.58
Exercise price range, upper limit (in dollar per share)	31.67
Number of shares, outstanding			391,568
Weighted average exercise price per share, outstanding (in dollar per share)			$ 37.78
Weighted average remaining contractual life, outstanding			7 years 1 month 28 days
Number of shares, vested			225,200,000
Weighted average exercise price per share, vested (in dollar per share)			$ 37.53
$26.86 - $30.58
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollar per share)	34.97
Exercise price range, upper limit (in dollar per share)	37.28
Number of shares, outstanding			213,744
Weighted average exercise price per share, outstanding (in dollar per share)			$ 49.97
Weighted average remaining contractual life, outstanding			7 years 6 months 20 days
Number of shares, vested			121,460,000
Weighted average exercise price per share, vested (in dollar per share)			$ 45.16
$31.67 - $37.28
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollar per share)	38.40
Exercise price range, upper limit (in dollar per share)	40.89
Number of shares, outstanding			101,125
Weighted average exercise price per share, outstanding (in dollar per share)			$ 76.21
Weighted average remaining contractual life, outstanding			9 years 9 months 10 days
Number of shares, vested			0
Weighted average exercise price per share, vested (in dollar per share)			$ 0
$40.68 - $40.89
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollar per share)	52.14
Exercise price range, upper limit (in dollar per share)	52.14
Number of shares, outstanding			78,550
Weighted average exercise price per share, outstanding (in dollar per share)			$ 78.85
Weighted average remaining contractual life, outstanding			9 years 3 months 19 days
Number of shares, vested			93,000
Weighted average exercise price per share, vested (in dollar per share)			$ 78.85
$52.14 - $52.14
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollar per share)	52.60
Exercise price range, upper limit (in dollar per share)	$ 52.60
Number of shares, outstanding			106,386
Weighted average exercise price per share, outstanding (in dollar per share)			$ 95.10
Weighted average remaining contractual life, outstanding			9 years 5 months 26 days
Number of shares, vested			104,000
Weighted average exercise price per share, vested (in dollar per share)			$ 95.10

Employee Stock and Benefit Pl_9

Employee Stock and Benefit Plans (Restricted Stock) (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 21, 2018	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based employee compensation			$ 30,090	$ 26,961	$ 20,149
Unrecognized employee compensation cost, period for recognition		2 years 1 month 10 days
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted (in shares)			548,245	1,326,849
Weighted-average grant date fair value (usd per share)			$ 75.44
Units vested and released in period (in shares)			525,375	368,367
Units outstanding and expected to vest (in shares)			1,226,883	1,410,588	587,333
Unrecognized employee compensation cost, period for recognition		2 years 7 months 28 days
Share-based Compensation Award, Tranche One | Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)	56,250
Share-based Compensation Award, Tranche Two | Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)	33,089
Award vesting period	3 years
Share-based Compensation Award, Tranche Three | Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)	33,088

Employee Stock and Benefit P_10

Employee Stock and Benefit Plans (Restricted Stock Units and Restricted Stock Awards Activity) (Details) - Restricted Stock Units - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Number of Shares
Beginning balance (in shares)	1,410,588	587,333
Granted (in shares)	548,245	1,326,849
Vested (in shares)	(525,375)	(368,367)
Canceled (in shares)	(206,575)	(135,227)
Ending balance (in shares)	1,226,883	1,410,588
Expected to vest as of December 31, 2016	898,637
Weighted-Average Grant Date Fair Value Per Share
Beginning balance (usd per share)	$ 40.34	$ 28.85
Granted (in shares)	75.44
Vested (in shares)	39.87
Canceled (in shares)	43.43
Ending balance (usd per share)	55.71	$ 40.34
Expected to vest as of December 31, 2016	$ 54.67

Employee Stock and Benefit P_11

Employee Stock and Benefit Plans - Share Repurchase Program and 401(k) Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Oct. 25, 2018	Feb. 05, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Repurchase Program, Authorized Amount				$ 100,000,000
Stock Repurchase Program, Additional Authorized Amount			$ 100,000,000
Stock Repurchased During Period, Value	$ 85,040,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	115,000,000
Contributions by the Company to the 401(k) plan	$ 1,200,000	$ 1,100,000
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Repurchased During Period, Shares	1,088,899
Stock Repurchased During Period, Value	$ 1,000

Other Income (Expense), Net (De

Other Income (Expense), Net (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Income and Expenses [Abstract]
Foreign exchange losses	$ (600)	$ (400)	$ (577)	$ (355)	$ (770)	$ (800)
Other expense			(224)	(181)	(202)
Other income (expense), net			$ (801)	$ (536)	$ (972)

Income Taxes (Income Before Pro

Income Taxes (Income Before Provision for (Benefit From) Income Taxes) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income (Loss) from Continuing Operations
Domestic									$ 50,010	$ 34,914	$ 28,982
Foreign									5,458	4,464	1,447
Income before income taxes	$ 14,805	$ 19,233	$ 11,779	$ 9,651	$ 10,381	$ 11,520	$ 9,369	$ 8,109	$ 55,468	$ 39,378	$ 30,429

Income Taxes (Provision For (Be

Income Taxes (Provision For (Benefit From) Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current
Federal	$ (90)	$ 22	$ 8,334
State	62	23	1,125
Foreign	1,988	1,471	963
Total current provision	1,960	1,516	10,422
Deferred
Federal	(3,449)	(1,650)	611
State	21	(996)	126
Foreign	(368)	68	46
Total deferred provision (benefit)	(3,796)	(2,578)	783
Provision for (benefit from) income taxes	$ (1,836)	$ (1,062)	$ 11,205

Income Taxes (Tax Rate Reconcil

Income Taxes (Tax Rate Reconciliation) (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
Federal statutory rate	21.00%	35.00%	35.00%
State taxes	(1.90%)	(2.10%)	2.10%
Stock-based compensation	(20.40%)	(58.10%)	2.40%
Foreign source income	(0.20%)	(0.20%)	0.90%
Change in valuation allowance	4.40%	2.80%	1.30%
Incremental federal rate benefit previously not recognized	0.00%	26.40%	0.00%
Federal and state research and development credit	(6.70%)	(5.30%)	(3.60%)
Other	0.50%	(1.20%)	(1.30%)
Provision for (benefit from) income taxes	(3.30%)	(2.70%)	36.80%

Income Taxes (Deferred Tax Asse

Income Taxes (Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Sep. 30, 2018
Deferred tax assets
Net operating loss carryforwards	$ 11,250	$ 8,947
Research and development credit carryforwards	16,901	11,493
Foreign tax credit carryforwards	2,209	1,149
Accrued liabilities	2,723	1,470
Deferred revenues	4,200	3,416
Intangible assets	0	405
Stock-based compensation	6,975	7,135
Other	174	196
Gross deferred tax assets	44,432	34,211
Valuation allowance	(9,100)	(5,773)
Net deferred tax assets	35,332	28,438
Deferred tax liabilities
Fixed assets	(8,161)	(3,372)
Intangible assets	(784)	0
Total deferred tax liabilities	(8,945)	(3,372)
Net deferred tax assets	$ 26,387	$ 25,066

Income Taxes (Unrecognized Tax

Income Taxes (Unrecognized Tax Benefits) (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits beginning balance	$ 5,112		$ 3,506
Gross increase for tax positions of prior years	279	$ 66	2
Gross decrease for tax positions of prior years	(227)	0	(15)
Gross increase for tax positions of current year	1,399	1,101	659
Lapse of statute of limitations	(157)	$ (126)	(81)
Total unrecognized tax benefits	$ 6,406		$ 4,071

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018	Jan. 01, 2017	Dec. 31, 2015
Income Tax [Line Items]
Tax Cuts and Jobs Act of 2017, Provisional income tax expense (benefit)	$ 10,400
Cumulative effect of a change in accounting principle related to stock-based compensation					$ 2,711
Provision for (benefit from) income taxes		$ (1,836)	$ (1,062)	$ 11,205
Valuation allowance	5,773	9,100
Increase in valuation allowance		3,300	2,100
Unrecognized tax benefits that would impact effective tax rate	3,500		$ 2,800				$ 2,400
State
Income Tax [Line Items]
Operating loss carryforwards		14,000
State | Research and Development Credits [Member]
Income Tax [Line Items]
Tax credit carryforward		10,900
Domestic Tax Authority [Member]
Income Tax [Line Items]
Operating loss carryforwards		48,400
Domestic Tax Authority [Member] | Research and Development Credits [Member]
Income Tax [Line Items]
Tax credit carryforward		$ 12,200
Foreign Tax Authority
Income Tax [Line Items]
Tax credit carryforward	$ 2,200
Accounting Standards Update 2016-09
Income Tax [Line Items]
Cumulative effect of a change in accounting principle related to stock-based compensation						$ 7,745
Retained earnings | Accounting Standards Update 2016-09
Income Tax [Line Items]
Cumulative effect of a change in accounting principle related to stock-based compensation						$ 7,745

Segment Information and Infor_3

Segment Information and Information about Geographic Area (Details) $ in Thousands	3 Months Ended						9 Months Ended		12 Months Ended
	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Sep. 30, 2018USD ($)segment	Sep. 30, 2017USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Segment Reporting Information [Line Items]
Number of operating segments (in segment) | segment							1
Revenues	$ 71,658	$ 68,153	$ 64,878	$ 59,490	$ 55,302	$ 53,121	$ 278,889	$ 230,828	$ 278,889	$ 230,828	$ 197,925	$ 197,925
Property and equipment, net	61,442						61,442		$ 61,442	58,557
United States
Segment Reporting Information [Line Items]
Revenues							185,887	162,681				139,743
Property and equipment, net	59,222						59,222			50,785
Foreign
Segment Reporting Information [Line Items]
Revenues							93,002	$ 68,147				$ 58,182
Property and equipment, net	$ 2,220						$ 2,220			$ 7,772

Net Income Per Share Attribut_3

Net Income Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								9 Months Ended		12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net income attributable to common stockholders - basic and diluted	$ 14,400	$ 23,469	$ 10,293	$ 9,142	$ 2,857	$ 8,452	$ 7,202	$ 21,930	$ 57,304	$ 40,440	$ 57,304	$ 40,440	$ 19,224	$ 19,224
Denominator:
Weighted-average shares used in computing net income per share - basic											38,876	37,443	35,247	35,247
Effect of potentially dilutive securities:
Common stock options (in shares)									2,401	2,262				3,052
RSUs (in shares)									620	366				70
Weighted - average shares used in computing net income (loss) per share attributable to common stockholders - diluted (in shares)									41,897	40,071	41,897	40,071	38,369	38,369
Basic (usd per share)	$ 0.37	$ 0.60	$ 0.26	$ 0.24	$ 0.07	$ 0.22	$ 0.19	$ 0.60		$ 1.08	$ 1.47	$ 1.08	$ 0.55	$ 0.55
Diluted (usd per share)	$ 0.35	$ 0.56	$ 0.24	$ 0.22	$ 0.07	$ 0.21	$ 0.18	$ 0.56		$ 1.01	$ 1.37	$ 1.01	$ 0.50	$ 0.50
Stock Options
Antidilutive Securities
Common stock options (in shares)									177	742				3,241
RSUs
Antidilutive Securities
Common stock options (in shares)									22	71				24

Quarterly Financial Informati_3

Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								9 Months Ended		12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Revenues		$ 71,658	$ 68,153	$ 64,878		$ 59,490	$ 55,302	$ 53,121	$ 278,889	$ 230,828	$ 278,889	$ 230,828	$ 197,925	$ 197,925
Cost of revenues											66,185	51,580	43,128
Gross profit											212,704	179,248	154,797
Operating expenses:
Research and development											53,255	42,816	36,591
Sales and marketing											70,039	63,855	58,985
General and administrative											39,049	35,334	29,114
Total operating expenses											162,343	142,005	124,690
Income from operations	$ 12,943	18,117	10,895	8,406	$ 9,729	10,849	9,009	7,656			50,361	37,243	30,107
Other income (expense), net	1,862	1,116	884	1,245	652	671	360	453			5,107	2,135	322
Income before income taxes	14,805	19,233	11,779	9,651	10,381	11,520	9,369	8,109			55,468	39,378	30,429
Provision for (benefit from) income taxes											(1,836)	(1,062)	11,205
Net income	$ 14,400	$ 23,469	$ 10,293	$ 9,142	$ 2,857	$ 8,452	$ 7,202	$ 21,930	$ 57,304	$ 40,440	$ 57,304	$ 40,440	$ 19,224	$ 19,224
Earnings Per Share [Abstract]
Basic (in usd per share)	$ 0.37	$ 0.60	$ 0.26	$ 0.24	$ 0.07	$ 0.22	$ 0.19	$ 0.60		$ 1.08	$ 1.47	$ 1.08	$ 0.55	$ 0.55
Diluted (usd per share)	$ 0.35	$ 0.56	$ 0.24	$ 0.22	$ 0.07	$ 0.21	$ 0.18	$ 0.56		$ 1.01	$ 1.37	$ 1.01	$ 0.50	$ 0.50

Schedule II Schedule of Valua_2

Schedule II Schedule of Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 816		$ 769
Charged to Costs and Expenses	85	$ 657	199
Deductions and Other	(218)	$ (543)	(266)
Balance at End of Year	$ 683		$ 702

Uncategorized Items - qlys-2018

Label	Element	Value
AOCI Attributable to Parent [Member]
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	$ (418,000)