Zix (ZIXI) 10-K 10 Mar 16 2015 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2015	Mar. 08, 2016	Jun. 30, 2015
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	FY
Trading Symbol	ZIXI
Entity Registrant Name	ZIX CORP
Entity Central Index Key	855,612
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		56,158,434
Entity Public Float			$ 261,306,219

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 28,664	$ 21,685
Receivables, net	498	1,452
Prepaid and other current assets	2,908	2,372
Deferred tax assets		1,763
Total current assets	32,070	27,272
Property and equipment, net	4,143	4,399
Goodwill	2,161	2,161
Deferred tax assets	48,912	49,892
Total assets	87,286	83,724
Current liabilities:
Accounts payable	370	506
Accrued expenses	4,697	2,930
Deferred revenue	23,182	21,587
Total current liabilities	28,249	25,023
Long-term liabilities:
Deferred revenue	839	898
Deferred rent	1,426	1,533
Total long-term liabilities	2,265	2,431
Total liabilities	$ 30,514	$ 27,454
Commitments and contingencies (Note 13)
Stockholders’ equity:
Preferred stock, $1 par value, 10,000,000 shares authorized; none issued and outstanding
Common stock, $0.01 par value, 175,000,000 shares authorized; 77,852,453 issued and 56,546,879 outstanding in 2015 and 75,017,775 issued and 56,980,789 outstanding in 2014	$ 767	$ 741
Additional paid-in capital	372,400	361,579
Treasury stock, at cost; 21,305,574 common shares in 2015 and 18,036,986 common shares in 2014	(82,243)	(66,882)
Accumulated deficit	(234,152)	(239,168)
Total stockholders’ equity	56,772	56,270
Total liabilities and stockholders’ equity	$ 87,286	$ 83,724

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 1	$ 1
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	175,000,000	175,000,000
Common stock, shares issued	77,852,453	75,017,775
Common stock, shares outstanding	56,546,879	56,980,789
Treasury stock, shares	21,305,574	18,036,986

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Revenues	$ 54,713	$ 50,347	$ 48,138
Cost of revenue	9,593	8,324	7,614
Gross margin	45,120	42,023	40,524
Research and development expenses	8,317	9,051	9,563
Selling, general and administrative expenses	28,887	26,222	21,646
Operating income	7,916	6,750	9,315
Other income (expense):
Investment and other income	244	183	132
Total other income	244	183	132
Income before income taxes	8,160	6,933	9,447
Income tax (expense) benefit	(3,144)	(2,830)	1,006
Net income	$ 5,016	$ 4,103	$ 10,453
Basic income per common share	$ 0.09	$ 0.07	$ 0.17
Diluted income per common share	$ 0.09	$ 0.07	$ 0.17
Weighted average shares outstanding
Basic common shares outstanding	56,421,833	57,948,864	61,139,035
Diluted common shares outstanding	57,476,006	58,966,625	62,526,507

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Treasury Stock [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2012	$ 61,245	$ 728	$ 355,747	$ (41,506)	$ (253,724)
Beginning balance, shares at Dec. 31, 2012		73,165,433
Issuance of common stock upon exercise of stock options	$ 1,705	$ 9	1,696
Issuance of common stock upon exercise of stock options, shares	839,263	839,263
Issuance of common stock upon vesting of restricted stock units		28,250
Issuance of restricted common stock, shares		385,000
Employee stock-based compensation costs	$ 1,591		1,711	(120)
Treasury repurchase program	(8,760)			(8,760)
Net income	10,453				10,453
Ending balance at Dec. 31, 2013	66,234	$ 737	359,154	(50,386)	(243,271)
Ending balance, shares at Dec. 31, 2013		74,417,946
Issuance of common stock upon exercise of stock options	$ 748	$ 4	744
Issuance of common stock upon exercise of stock options, shares	407,829	407,829
Issuance of common stock upon vesting of restricted stock units		52,000
Issuance of restricted common stock, shares		140,000
Employee stock-based compensation costs	$ 1,424		1,681	(257)
Treasury repurchase program	(16,239)			(16,239)
Net income	4,103				4,103
Ending balance at Dec. 31, 2014	$ 56,270	$ 741	361,579	(66,882)	(239,168)
Ending balance, shares at Dec. 31, 2014		75,017,775
Beginning balance, shares at Dec. 31, 2014	75,017,775
Issuance of common stock upon exercise of stock options	$ 8,674	$ 26	8,648
Issuance of common stock upon exercise of stock options, shares	2,668,928	2,668,928
Issuance of common stock upon vesting of restricted stock units		65,750
Issuance of restricted common stock, shares		100,000
Employee stock-based compensation costs	$ 1,812		2,173	(361)
Treasury repurchase program	(15,000)			(15,000)
Net income	5,016				5,016
Ending balance at Dec. 31, 2015	$ 56,772	$ 767	$ 372,400	$ (82,243)	$ (234,152)
Ending balance, shares at Dec. 31, 2015		77,852,453

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating activities:
Net income	$ 5,016	$ 4,103	$ 10,453
Non-cash items in net income:
Depreciation and amortization	2,152	1,623	1,466
Employee stock-based compensation expense	2,173	1,681	1,711
Changes in deferred taxes	2,743	2,398	(1,401)
Changes in operating assets and liabilities:
Receivables	954	872	(1,357)
Prepaid and other assets	(536)	(334)	(341)
Accounts payable	(81)	(1)	(103)
Deferred revenue	1,536	2,127	1,986
Accrued and other liabilities	1,660	848	884
Net cash provided by operating activities	15,617	13,317	13,298
Investing activities:
Purchases of property and equipment	(1,951)	(3,402)	(1,593)
Net cash used in investing activities	(1,951)	(3,402)	(1,593)
Financing activities:
Proceeds from exercise of stock options	8,674	748	1,705
Treasury stock	(15,361)	(16,496)	(8,880)
Net cash used in financing activities	(6,687)	(15,748)	(7,175)
Increase (decrease) in cash and cash equivalents	6,979	(5,833)	4,530
Cash and cash equivalents, beginning of year	21,685	27,518	22,988
Cash and cash equivalents, end of year	$ 28,664	$ 21,685	$ 27,518

Company Overview

Company Overview	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Company Overview	1. Company Overview Zix Corporation (“ZixCorp,” the “Company,” “we,” “our,” “us”) provides email encryption, data loss prevention (“DLP”) and Bring-Your-Own-Device (“BYOD”) solutions to meet the data protection and compliance needs of organizations primarily in the healthcare, financial services, and government sectors.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation — The accompanying consolidated financial statements include the accounts of all our wholly-owned subsidiaries and are prepared in accordance with accounting principles generally accepted in the United States of America. All inter-company accounts and transactions have been eliminated in consolidation. Use of Estimates — The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amount of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reported period. Our significant estimates include primarily those required in the valuation or impairment analysis of goodwill, property and equipment, revenue recognition, allowances for doubtful accounts, stock-based compensation, litigation accruals, valuation allowances for deferred tax assets and tax accruals. Although we believe that adequate accruals have been made for unsettled issues, additional gains or losses could occur in future years from resolutions of outstanding matters. Actual results could differ materially from original estimates. Cash Equivalents — Cash investments with maturities of three months or less when purchased are considered cash equivalents. Fair Value of Financial Instruments —The Company does not measure the fair value of any financial instrument other than cash equivalents, options, and other equity awards. The carrying values of other financial instruments (receivables and accounts payable) are not recorded at fair value but approximate fair values primarily due to their short-term nature. The carrying values of other current assets and accrued expenses are also not recorded at fair value, but approximate fair values primarily due to their short-term nature. Valuation of Property and Equipment — The accounting policies and estimates relating to property and equipment are considered significant because of the potential impact that impairment, obsolescence, or change in an asset’s useful life could have on the Company’s operating results. We record an impairment charge on the assets to be held and used when we determine based upon certain triggering events that the carrying value of property and equipment may not be recoverable based on expected undiscounted cash flows attributable to such assets. The amount of a potential impairment is determined by comparing the carrying amount of the asset to either the value determined from a projected discounted cash flow method, using a discount rate that is considered to be commensurate with the risk inherent in the Company’s current business model or the estimated fair market value. Assumptions are made with respect to future net cash flows expected to be generated by the related asset. An impairment charge would be recorded for an amount by which the carrying value of the asset exceeded the discounted projected net cash flows or estimated fair market value. Also, even where a current impairment charge is not necessary, the remaining useful lives are evaluated. No impairment was recorded for any of the periods presented. Property and equipment are recorded at cost and depreciated or amortized using the straight-line method over their estimated useful lives as follows: computer and office equipment and software — three years; leasehold improvements — the shorter of five years or the lease term; and furniture and fixtures — five years. Goodwill — We account for the valuation of goodwill and other intangible assets after classifying intangible assets into three categories: (1) intangible assets with finite lives subject to amortization; (2) intangible assets with indefinite lives not subject to amortization; and (3) goodwill. For intangible assets with finite lives, tests for impairment must be performed if conditions exist that indicate the carrying value may not be recoverable. For intangible assets with indefinite lives and goodwill, tests for impairment must be performed at least annually or more frequently if events or circumstances indicate that assets might be impaired. Goodwill was $2.2 million, or 2% and 3% of total assets for the years ended December 31, 2015 and 2014, respectively. Our goodwill is not being amortized, but we do evaluate the goodwill for impairment annually in the fourth quarter, or when there is reason to believe that the value has been diminished or impaired. Evaluations for possible impairment are based upon a comparison of the estimated fair value of the reporting unit to which the goodwill has been assigned, versus the sum of the carrying value of the assets and liabilities of that unit including the assigned goodwill value. The fair values used in this evaluation are estimated based on the Company’s market capitalization, which is based on the outstanding stock and market price of the stock. Impairment is deemed to exist if the net book value of the unit exceeds its estimated fair value. No impairment was recorded for any of the periods presented. Deferred Tax Assets — Deferred tax assets are recognized if it is “more likely than not” that the benefit of the deferred tax asset will be realized on future federal or state income tax returns. At December 31, 2015, we provided a valuation allowance against a significant portion, $46.1 million, of our accumulated U.S. deferred tax assets, reflecting our historical losses and the uncertainty of future taxable income sufficient to utilize net operating loss carryforwards prior to their expiration. Our total deferred tax asset not subject to a valuation allowance is valued at $48.9 million, and consists of $41.8 million for federal net operating loss carryforwards, $4.1 million relating to temporary timing differences between GAAP and tax-related expense, $1.8 million relating to U.S. state income tax credits and $1.2 million related to Alternative Minimum Tax credits. If U.S. taxable income increases from its current level in a future period or if the facts and circumstances on which our estimates and assumptions are based were to change, thereby impacting the likelihood of realizing the deferred tax assets, judgment would have to be applied in determining the amount of valuation allowance no longer required. Reversal of all or a part of this valuation allowance could have a significant positive impact on operating results in the period that it becomes more likely than not that certain of the Company’s deferred tax assets will be realized. Alternatively, should our future income decrease from current levels, a resulting increase to all or a part of this valuation allowance could also have a significant negative impact on our operating results. Leases — A leased asset whose lease terms meet the criteria for capitalization is recorded as an asset and depreciated. If a lease does not meet the criteria for capitalization, it is classified as an operating lease and payments are recorded as rent expense. For 2015 and 2014 we had no leases that qualified as capital leases. Lease renewal options which we are “reasonably assured” of using and the related payments are taken into account when initially classifying and recording the lease as a capital lease obligation or as straight-line rent if an operating lease. Funds provided by the lessor for leasehold improvements are recorded as a deferred lease incentive and amortized as a reduction of rent expense over the lease term. Revenue Recognition — We develop, market, and support applications that connect, protect and deliver information in a secure manner. We generate our sales through both a direct sales team and, increasingly, through our channel partners. We derive our revenue from subscription fees for rights related to the use of our software. Software subscription terms typically range from one to three years. Revenue is recognized when all of the following criteria have been met: · persuasive evidence of an arrangement exists, · delivery has occurred or services have been rendered, · the price is fixed and determinable, and · collectability is probable. We record our revenue net of any value added or sales tax. Discounts provided to customers are recorded as reductions in revenue. We have determined that substantially all of our revenue arrangements are in the scope of the software revenue recognition rules. Multiple elements in our software arrangements are sold as a single unit consisting of the following elements: (i) subscription licensed software delivered to the customer’s site, (ii) ongoing customer support and, (iii) access to our hosted encryption network (Zix encryption network) during the term of the agreement. (i) Software at the customer site performs critical functions of the email encryption process and is the predominant element in our arrangements. Actions performed by the software at the customer site include identifying when encryption is needed through the use of filters and lexicons, determining the best method of delivery (BMOD) by examining secure connection options and selecting the BMOD. BMOD is a key marketing differentiator for us and is defined as the most secure and easiest method to deliver encrypted email. Customers can install the software on their own hardware or we can deliver to the customer site hardware that we own. In recent years more customers have opted to have the software installed on their own hardware, and as a result the number of Zix supplied hardware devices has declined. Any hardware provided as part of our services primarily included manufacturer provided warranty provisions. We recorded no warranty expense in any of the presented periods. ( ii ) Customer support includes unspecified software upgrades, updates and bug fixes and access to live technical support technicians and on-line knowledge resources ( ii i) The Zix encryption network includes access to our central network which facilitates transparent encrypted email exchange among all of our customers by providing public encryption keys (asymmetrical encryption requires two keys- a public key provided by the central network and a private key generated by the software at the customer site). The delivered software element is essential to the functionality and utility of this central network. The network also enables our customers to send encrypted emails to non-Zix customer recipients through a portal. A small portion of our revenue (less than 5% in 2015) is derived from hosted email encryption solutions. We apply general revenue recognition guidance to these hosted arrangements. In all revenue arrangements we cannot determine vendor specific objective evidence (VSOE) and we cannot establish separate units of accounting for the multiple elements of our arrangements that are bundled and sold as one unit. All revenue arrangements are sales of subscription based (i.e. time-based) licenses. We defer revenue until the software is delivered and the service is deployed. Upon deployment, we commence revenue recognition and revenue is recognized ratably over the subscription period generally ranging from one to three years. Software Development Costs —Costs incurred in the development and testing of subscription software products related to research, project planning, training, maintenance and general and administrative activities, and overhead costs are expensed as incurred. The costs of relatively minor upgrades and enhancements to the software are also expensed as incurred. Costs for the development of new software solutions and substantial enhancements to existing software solutions are expensed as incurred until technological feasibility has been established, at which time any additional costs would be capitalized. No research and development costs have been capitalized because we believe that technological feasibility is established concurrent with general release to customers. Research and development costs associated with software developed for internal use on behalf of our customers are capitalized. To date, capitalized costs for software developed for internal use on behalf of our customers were not material. Advertising Expense — Advertising costs are expensed as incurred. Our operations include advertising expense of $2.1 million, $2.9 million, and $959 thousand in 2015, 2014, and 2013, respectively. Stock-Based Compensation — We currently use the straight-line amortization method for recognizing stock option and restricted stock compensation costs. The measurement and recognition of compensation expense for all share-based payment awards made to our employees and directors are based on the estimated fair value of the awards on the grant dates. The grant date fair value is estimated using either an option-pricing model which is consistent with the terms of the award or a market observed price, if such a price exists. Such cost is recognized over the period during which an employee or director is required to provide service in exchange for the award, i.e., “the requisite service period” (which is usually the vesting period). We also estimate the number of instruments that will ultimately be earned, rather than accounting for forfeitures as they occur. Earnings Per Share (“EPS”) — Basic EPS is based on the weighted average number of common shares outstanding during each period. Diluted EPS adjusts Basic EPS for the effects of dilutive common stock equivalents outstanding during each period using the treasury stock method. New Accounting Standards Revenue Recognition In May 2014, the FASB issued Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (ASU 2014-09), which supersedes most current revenue recognition guidance under U.S. GAAP. The core principle of ASU 2014-09 is to recognize revenues when promised goods or services are transferred to customers in an amount that reflects the consideration to which an entity expects to be entitled for those goods or services. ASU 2014-09 defines a five step process to achieve this core principle and, in doing so, more judgment and estimates may be required within the revenue recognition process than are required under existing U.S. GAAP. The standard is effective for us beginning 2018, and requires using either of the following transition methods: (i) a full retrospective approach reflecting the application of the standard in each prior reporting period with the option to elect certain practical expedients, or (ii) a retrospective approach with the cumulative effect of initially adopting ASU 2014-09 recognized at the date of adoption (which includes additional footnote disclosures). We are currently evaluating the impact of our pending adoption of ASU 2014-09 on our consolidated financial statements and have not yet determined the method by which we will adopt the standard in 2018. Classification of Deferred Taxes In November 2015, the FASB issued guidance that requires entities to present deferred tax assets and deferred tax liabilities as noncurrent on the balance sheet. The standard will be effective for annual periods beginning after December 15, 2016, but may be adopted early. This new guidance did not have a material impact on our consolidated financial statements. We have chosen to prospectively apply the guidance to our 2015 balance sheet. Prior year balances were not retroactively adjusted.

Stock Options and Stock-based E

Stock Options and Stock-based Employee Compensation	12 Months Ended
	Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock Options and Stock-based Employee Compensation	3. Stock Options and Stock-based Employee Compensation Below is a summary of common stock options outstanding at December 31, 2015: Authorized Shares Options Outstanding Options Vested Available for Grant Employee and Director Stock Option Plans: 2001 Stock Option Plan 2,525,000 11,400 11,400 — 2001 Employee Stock Option Plan 300,000 4,020 4,020 — 2004 Stock Option Plan 5,000,000 1,258,069 1,258,069 — 2006 Director’s Stock Option Plan 1,100,000 209,500 209,500 — 2012 Incentive Plan 6,300,000 291,563 153,249 3,751,308 Total 15,225,000 1,774,552 1,636,238 3,751,308 Under all of our stock option plans, new shares are issued when options are exercised. Employee and Director Stock Option Plans We have non-qualified stock options outstanding to employees and directors under various stock option plans. The plans require the exercise price of options granted under these plans to equal or exceed the fair market value of the Company’s common stock on the date of grant. The options, subject to termination of employment, generally expire ten years from the date of grant. Historically, our employee options typically vested pro-rata and quarterly over three years. Option grants to employees, officers and directors frequently contain accelerated vesting provisions upon the occurrence of a change of control, as defined in the applicable option agreements. Under the terms of the 2012 Incentive Plan adopted by the Company’s Board of Directors on April 13, 2012 (the “2012 Plan”), 2,700,000 shares are available for issuance, plus a number of additional shares (not to exceed 1,327,000) underlying options outstanding under certain of the Company’s prior equity plans that thereafter terminate or expire unexercised, or are cancelled, forfeited, or lapse for any reason. Our shareholders approved an Amended and Restated 2012 Incentive Plan during our annual meeting held June 24, 2015, increasing the number of shares available for grant by 3,600,000. Awards issued under the 2012 Plan typically vest pro-rata and quarterly over four years. Accounting Treatment We use the straight-line amortization method for recognizing stock option compensation costs. Our share-based awards include stock options, restricted stock awards (“RSAs”), restricted stock units (“RSUs”), and performance units (“PUs”). For the twelve months ended December 31, 2015, 2014, and 2013, respectively, the total stock-based compensation expense resulting from stock options, RSAs, RSUs, and PUs was recorded to the following line items of our consolidated statements of income: Year Ended December 31, (In thousands) 2015 2014 2013 Cost of revenue $ 182 $ 180 $ 172 Research and development expenses 242 237 212 Selling, general and administrative expenses 1,749 1,264 1,327 Stock-based compensation expense $ 2,173 $ 1,681 $ 1,711 Our 2015 stock-based compensation expense includes $540 thousand related to the accelerated vesting of awards related to our CEO departure. A deferred tax asset of $625 thousand, $462 thousand and $483 thousand, resulting from stock-based compensation expense associated with awards relating to the Company’s U.S. operations, was recorded for the twelve months ended December 31, 2015, 2014 and 2013, respectively. As of December 31, 2015, there was $2.1 million of total unrecognized stock-based compensation related to non-vested share-based compensation awards granted under the stock option plans. This cost is expected to be recognized over a weighted average period of 1.5 years. We used the Black-Scholes Option Pricing Model (“BSOPM”) to determine the fair value of option grants made during 2013. No options were granted in 2014 or 2015. On January 1, 2006, we elected to use the “simplified” method to calculate the estimated life of options granted to employees. The Company continued to use the “simplified” method for all options granted through 2013. The Company has elected to use the “historical” method to calculate the estimated life of any options that may be granted in the future. The expected stock price volatility was calculated by averaging the historical volatility of the Company’s common stock over a term equal to the expected life of the options. The following weighted average assumptions were applied in determining the fair value of options granted during the respective periods: Year Ended December 31, 2015 2014 2013 Risk-free interest rate — — 1.05 % Expected option life (years) — — 5.8 Expected stock price volatility — — 69 % Expected dividend yield — — — Fair value of options granted — — $ 1.99 The assumptions used in the BSOPM valuation are critical as a change in any given factor could have a material impact on the financial results of the Company. The weighted average grant-date fair value of awards of restricted stock and RSU’s is based on quoted market price of the Company’s common stock on the date of grant. Stock Option Activity There were 2,668,928 stock options exercised for the twelve months ended December 31, 2015. As a result of these stock option exercises, there was $19 thousand in excess tax benefits recorded in 2015. For the comparative period in 2014, there were 407,829 stock option exercises. The following is a summary of all stock option transactions for the three years ended December 31, 2015: Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Yrs) Outstanding at January 1, 2013 7,684,776 $ 4.28 Granted at market price 150,000 $ 3.27 Cancelled or expired (247,139 ) $ 5.15 Exercised (839,263 ) $ 2.03 Outstanding at December 31, 2013 6,748,374 $ 4.50 Granted at market price — — Cancelled or expired (1,850,036 ) $ 7.71 Exercised (407,829 ) $ 1.83 Outstanding at December 31, 2014 4,490,509 $ 3.42 Granted at market price — — Cancelled or expired (47,029 ) $ 4.69 Exercised (2,668,928 ) $ 3.25 Outstanding at December 31, 2015 1,774,552 $ 3.65 3.41 Options exercisable at December 31, 2015 1,636,238 $ 3.73 3.13 At December 31, 2015, all 1,774,552 options outstanding and all 1,636,238 options exercisable had an exercise price lower than the market value of the Company’s common stock. The aggregate intrinsic value of these options was $2.5 million and $2.2 million, respectively. At December 31, 2014, we had 2,207,201 options outstanding and 1,852,423 options exercisable in which the exercise price was lower than the market value of the Company’s common stock. The aggregate intrinsic value of these options was $2.4 million and $2.1 million, respectively. The total intrinsic value of options exercised during the years ended December 31, 2015 and 2014, was $4.4 million and $716 thousand, respectively. Summarized information about stock options outstanding at December 31, 2015, is as follows: Options Outstanding Options Exercisable Range of Exercise Prices Number Outstanding Weighted Average Remaining Contractual Life Weighted Average Exercise Price Number Exercisable Weighted Average Exercise Price $1.11 - $1.99 204,050 2.15 $ 1.41 204,050 $ 1.41 $2.00 - $3.49 567,142 5.61 $ 2.59 428,828 $ 2.54 $3.50 - $4.99 1,003,360 2.37 $ 4.71 1,003,360 $ 4.71 1,774,552 3.41 $ 3.65 1,636,238 $ 3.73 There were 4,135,731 and 5,908,498 exercisable options at December 31, 2014 and 2013, respectively. Restricted Stock Activity The following is a summary of all restricted stock activity during the three years ended December 31, 2015: Restricted Shares Weighted Average Fair Value Non-vested at January 1, 2013 351,000 $ 2.49 Granted at market price 385,000 $ 3.45 Vested (87,750 ) $ 2.49 Cancelled — — Non-vested restricted stock at December 31, 2013 648,250 $ 3.06 Granted at market price 140,000 $ 4.66 Vested (184,000 ) $ 2.99 Cancelled — — Non-vested restricted stock at December 31, 2014 604,250 $ 3.45 Granted at market price 100,000 $ 5.18 Vested (240,750 ) $ 3.35 Cancelled (40,250 ) $ 3.57 Non-vested restricted stock at December 31, 2015 423,250 $ 3.91 As a result of these vesting RSA’s $84 thousand in excess tax benefits was recorded in 2015. Restricted Stock Unit Activity The following is a summary of all RSU activity during the three years ended December 31, 2015: Restricted Stock Units Weighted Average Fair Value Non-vested at January 1, 2013 113,000 $ 2.49 Granted at market price 95,000 $ 3.45 Vested (28,250 ) $ 2.49 Cancelled — — Non-vested restricted stock units at December 31, 2013 179,750 $ 3.00 Granted at market price 55,000 $ 4.66 Vested (52,000 ) $ 2.93 Cancelled — — Non-vested restricted stock units at December 31, 2014 182,750 $ 3.52 Granted at market price 215,000 $ 3.88 Vested (65,750 ) $ 3.29 Cancelled (32,500 ) $ 3.88 Non-vested restricted stock units at December 31, 2015 299,500 $ 3.79 Performance Unit Activity The following is a summary of all PU activity during the two years ended December 31, 2015: Restricted Stock Units Weighted Average Fair Value Non-vested at January 1, 2014 — — Granted at market price 100,000 $ 4.66 Vested — — Forfeited (100,000 ) $ 4.66 Non-vested restricted stock units at December 31, 2014 — — Granted at market price 215,000 $ 3.88 Vested — — Forfeited (32,500 ) $ 3.88 Non-vested restricted stock units at December 31, 2015 182,500 $ 3.88 In February 2016 the Compensation Committee of our board of directors approved the achievement of certain 2015 performance metrics, resulting in the vesting of 27,428 PUs during the first quarter 2016. An additional 10,350 PU’s vested in the first quarter 2016 related to our CEO separation. The weighted average grant-date fair value of awards of restricted stock and RSUs (collectively “restricted stock”) and PUs is based on the quoted market price of the Company’s common stock on the date of grant.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	12 Months Ended
	Dec. 31, 2015
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	4. Supplemental Cash Flow Information Supplemental information relating to taxes and noncash activities: Year Ended December 31, (In thousands) 2015 2014 2013 Income tax payments $ 332 $ 426 $ 217 Payables related to purchases of capitalized assets $ 55 $ (12 ) $ (97 ) Excess tax benefit on exercise and vesting of employee equity awards $ 103 $ 168 $ 427

Receivables, Net

Receivables, Net	12 Months Ended
	Dec. 31, 2015
Receivables [Abstract]
Receivables, Net	5. Receivables, net (In thousands) December 31, 2015 2014 Gross accounts receivables $ 7,882 $ 8,116 Allowance for returns and doubtful accounts (59 ) (108 ) Unpaid portion of deferred revenue (7,325 ) (6,556 ) Note receivable 458 458 Allowance for note receivable (458 ) (458 ) Receivables, net $ 498 $ 1,452 Our gross accounts receivables for the year ended 2014 included $318 thousand associated with a tenant improvement allowance received as an incentive when we renewed the lease for our Dallas headquarters in 2013. The tenant improvement receivable was collected in full in the first quarter 2015. The allowance for doubtful accounts includes all specific accounts receivable which we believe are likely not collectable based on known information. In addition, we record 2.5% of all accounts receivable greater than 90 days past due, net of those accounts specifically reserved, as a general allowance against accounts that could potentially become uncollectible. The reduction for deferred revenue represents future customer service or maintenance obligations which have been billed to customers, but remain unpaid as of the respective balance sheet dates. Deferred revenue on our consolidated balance sheets represents future customer service or maintenance obligations which have been billed and collected as of the respective balance sheet dates. The note receivable represents the remaining outstanding balance of an original note related to the sale of a product line in 2005 in the amount of $540 thousand. This was fully reserved at the time of the sale as the note’s collectability was not assured. The note receivable is fully reserved at December 31, 2015.

Prepaid and other current asset

Prepaid and other current assets	12 Months Ended
	Dec. 31, 2015
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid and other current assets	6. Prepaid and other current assets (In thousands) December 31, 2015 2014 Prepaid insurance, maintenance, software licenses and other $ 2,596 $ 1,954 Deferred commissions 364 443 Tax-related (52 ) (25 ) Prepaid and other current assets $ 2,908 $ 2,372

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2015
Property Plant And Equipment [Abstract]
Property and Equipment	7. Property and Equipment (In thousands) December 31, 2015 2014 Computer and office equipment and software $ 23,797 $ 23,013 Leasehold improvements 6,663 6,398 Furniture and fixtures 1,969 1,916 32,429 31,327 Less accumulated depreciation and amortization (28,286 ) (26,928 ) Total Property and Equipment $ 4,143 $ 4,399 Our operations include depreciation and amortization expense related to property and equipment of $2.2 million, $1.6 million, and $1.5 million in 2015, 2014, and 2013, respectfully.

Goodwill

Goodwill	12 Months Ended
	Dec. 31, 2015
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill	8. Goodwill At December 31, 2015 and 2014, we had goodwill totaling $2.2 million. We evaluate goodwill for impairment annually in the fourth quarter, or when there is reason to believe that the value has been diminished or impaired. There were no impairment indicators to the goodwill recorded as of December 31, 2015.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2015
Payables And Accruals [Abstract]
Accrued Expenses	9. Accrued Expenses December 31, (In thousands) 2015 2014 Employee compensation and benefits $ 3,028 $ 1,061 Professional fees 467 473 Taxes 399 378 Other 803 1,018 Total accrued expenses $ 4,697 $ 2,930

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value Measurements	10. Fair Value Measurements FASB guidance regarding fair value measurement establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value. These tiers include: Level 1, defined as observable inputs such as quoted prices in active markets for identical assets or liabilities; Level 2, defined as inputs other than quoted prices for similar assets and liabilities in active markets that are either directly or indirectly observable; and Level 3, defined as unobservable inputs for which little or no market data exists, therefore requiring an entity to develop its own assumptions.

Earnings Per Share and Potentia

Earnings Per Share and Potential Dilution	12 Months Ended
	Dec. 31, 2015
Earnings Per Share [Abstract]
Earnings Per Share and Potential Dilution	11. Earnings Per Share and Potential Dilution Basic earnings per share are computed using the weighted average number of common shares outstanding for the period. The dilutive effect of potential common shares outstanding is included in diluted earnings per share. The computations for basic and diluted earnings per share for the years ended December 31, 2015, 2014, and 2013, are as follows: Year Ended December 31, 2015 2014 2013 Basic weighted average shares 56,421,833 57,948,864 61,139,035 Effect of dilutive securities: Employee and director stock options 741,002 782,659 1,095,227 Restricted Stock 172,126 181,219 225,741 RSUs 100,353 53,832 66,504 PUs 40,692 51 — Potential dilutive common shares 57,476,006 58,966,625 62,526,507 For the years ended December 31, 2015, 2014, and 2013, weighted average shares related to certain stock options of 1,005,328, 3,240,594, and 4,054,261 respectively, were excluded from the calculation of diluted earnings per share because the stock options were anti-dilutive. Anti-dilutive restricted stock, RSUs, and PUs of 56,542, 33,512, and 24,486, respectively, were also excluded from the calculation for the year ended December 31, 2015. Anti-dilutive restricted stock, RSUs, and PUs of 147,292, 50,833, and 33,333, respectively, were excluded from the calculation for the year ended December 31, 2014. Anti-dilutive restricted stock and RSUs of 31,281, and 7,719, respectively, were excluded from the calculation for the year ended December 31, 2013.

Significant Customers

Significant Customers	12 Months Ended
	Dec. 31, 2015
Text Block [Abstract]
Significant Customers	12. Significant Customers In 2015, 2014, and 2013, no single customer accounted for 10% or more of our revenues.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2015
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	13. Commitments and Contingencies Leases We lease office facilities under non-cancelable operating lease agreements. Our operations include rent expense for these operating leases of $1.4 million in each of 2015 and 2014, and $1.3 million in 2013. The lease of our headquarters facility in Dallas expires in 2024. A summary of our fixed contractual obligations and commitments at December 31, 2015, is as follows: (In thousands) 2016 2017 2018 2019 2020 Thereafter Total Operating leases $ 1,369 $ 1,131 $ 1,027 $ 1,030 $ 1,035 $ 4,125 $ 9,717 Claims and Proceedings We are subject to legal proceedings, claims, and litigation against our business. While the outcome of these matters is currently not determinable and the costs and expenses of defending these matters may be significant, we currently do not expect that the ultimate costs to resolve these matters will have a material adverse effect on our consolidated financial statements.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income Taxes	14. Income Taxes Components of the income taxes are as follows: (In thousands) 2015 2014 2013 Current: U.S. $ 58 $ 67 $ 124 State 196 240 148 Foreign 146 125 123 Deferred Federal 2,744 2,396 (1,400 ) State — — — Foreign — 2 (1 ) Income tax expense (benefit) $ 3,144 $ 2,830 $ (1,006 ) A reconciliation of the expected U.S. tax expense (benefit) to income taxes is as follows: (In thousands) 2015 2014 2013 Expected tax (benefit) expense at U.S. statutory rate $ 2,775 $ 2,357 $ 3,212 Decrease in valuations allowance- Operations — — (2,650 ) Decrease in valuations allowance- Other — — (1,400 ) Nondeductible expense and nontaxable income 133 127 (370 ) State income taxes 129 224 98 Foreign income taxes 146 127 122 Other (39 ) (5 ) (18 ) Income tax expense (benefit) $ 3,144 $ 2,830 $ (1,006 ) Deferred income taxes reflect the net 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. Components of our U.S. deferred income taxes as of December 31, 2015 and 2014 are as follows: (In thousands) 2015 2014 Deferred tax assets: Reserves- Other $ 156 $ 325 U.S. net operating loss carryforwards 84,591 86,382 State net operating loss carryforwards 281 281 Tax credit carryforwards 6,030 5,863 Stock-based compensation 1,767 2,623 Intangible assets 98 538 Depreciable assets 1,518 1,461 Other assets 1,272 712 Total deferred tax assets 95,713 98,185 Deferred tax liabilities: Prepaid expenses (671 ) (496 ) Total deferred tax assets 95,042 97,689 Less valuation allowance (46,134 ) (46,038 ) Net deferred tax assets $ 48,908 $ 51,651 The Company has partially reserved its U.S. net deferred tax assets in 2015 and 2014 due to the uncertainty of future taxable income. The Company has U.S. net operating loss carryforwards of approximately $249 million which begin to expire in 2020. The Company has state credits that net of federal tax expense total $1.7 million which can be utilized through 2027 and state net operating losses that have various expiration dates. The Company also has tax credit carryforwards of approximately $4.3 million consisting of business tax credits which begin to expire in 2016 and alternative minimum tax credits which do not expire. In 2010, the Company achieved positive earnings and successfully discontinued operations of its e‑Prescribing segment. Based on the weight of available objective evidence, including the Company’s history of positive earnings from continuing operations and successful exit from e-Prescribing, management believed that it was more likely than not that a portion of the deferred tax asset would be realized. Accordingly, the Company reduced its valuation allowance by $4.1 million in 2013. We have determined that utilization of existing net operating losses against future taxable income is not limited by Section 382 of the Internal Revenue Code. Future ownership changes, however, may limit the company's ability to fully utilize its existing net operating loss carryforwards against any future taxable income. The Company or one of our subsidiaries files income tax returns in the U.S. federal jurisdiction and various states and in the Canadian federal and provincial jurisdictions. We have not taken a tax position that, if challenged, would have a material effect on the financial statements or the effective tax rate for the twelve-months ended December 31, 2015, or during the prior three years. We have determined it is not reasonably possible for the amounts of unrecognized tax benefits to significantly increase or decrease within the next twelve months. We are currently subject to a three-year statute of limitations by major tax jurisdictions.

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2015
Postemployment Benefits [Abstract]
Employee Benefit Plan	15. Employee Benefit Plan 401(k) Plan — We have a retirement savings plan structured under Section 401(k) of the Internal Revenue Code covering substantially all of our U.S. employees. Under the plan, contributions are voluntarily made by employees, and we may provide contributions based on the employees’ contributions. Our operating income includes $389 thousand, $354 thousand, and $297 thousand, in 2015, 2014, and 2013, respectively, for net contributions from operations to this plan.

ZixCorp Repurchase Program

ZixCorp Repurchase Program	12 Months Ended
	Dec. 31, 2015
Equity [Abstract]
ZixCorp Repurchase Program	During the year ended December 31, 2015, the Company repurchased 3,185,340 shares at an aggregate cost of $15.0 million. This completed the $15 million share repurchase authorized by our board of directors in May 2015. On May 11, 2015, the board of directors also approved the termination of the $10 million share repurchase program announced in January 2015. No shares were repurchased under that program. During the year ended December 31, 2014, we repurchased a total of 4,070,195 shares at an aggregate cost of $16.2 million, as authorized by our board of directors under a $15 million share repurchase program announced November 6, 2013, and a $10 million repurchase program announced July 30, 2014. The 2014 repurchase activity completed both programs. During the year ended December 31, 2013, we repurchased 1,976,900 shares at an aggregate cost of $8.8 million under the $15 million repurchase program announced November 2013.

Quarterly Results of Operations

Quarterly Results of Operations (Unaudited)	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Quarterly Results of Operations (Unaudited)	17. Quarterly Results of Operations (Unaudited) The following is a summary of the quarterly results of operations for the years ended December 31, 2015 and 2014: Quarter Ended (In thousands except per share data) March 31 June 30 September 30 December 31 2015 Revenues $ 13,073 $ 13,302 $ 14,011 $ 14,327 Gross margin 10,860 10,873 11,582 11,805 Net income 1,176 1,115 1,927 798 Basic net income per common share* 0.02 0.02 0.03 0.01 Diluted net income per common share* 0.02 0.02 0.03 0.01 2014 Revenues $ 12,162 $ 12,615 $ 12,705 $ 12,865 Gross margin 10,137 10,583 10,643 10,660 Net income 1,059 977 1,163 904 Basic net income per common share* 0.02 0.02 0.02 0.02 Diluted net income per common share* 0.02 0.02 0.02 0.02 * Net income per share is calculated independently for each quarter. The sum of Net income per share for each quarter may not equal the total Net income per share for the year due to rounding differences.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2015
Subsequent Events [Abstract]
Subsequent Events	18. Subsequent Events On January 5, 2016, the Company’s board of directors approved a share repurchase program that enables the Company to purchase up to $15 million of its shares of common stock. The amount and timing of specific repurchases are subject to market conditions, applicable to legal requirements and other factors. Any share purchases would be funded from existing cash resources and may be suspended or discontinued at any time. The share repurchase program will expire on September 30, 2016. On January 19, 2016, the Company’s board of directors appointed David J. Wagner to the positions of Chief Executive Officer and President of Zix Corporation and elected Mr. Wagner to the board. Former CEO and President Richard D. Spurr stepped down from those positions, effective January 19, 2016. The severance costs related to our CEO transition were recorded to general and administrative expense during the year ended December 31, 2015. No additional charges associated with this transition are expected in 2016. Mr. Spurr remains a member of the board of directors, the size of which has increased from five to six members. Both Mr. Wagner and Mr. Spurr will serve on the board for terms that will expire at the 2016 annual meeting of the Company’s shareholders.

Summary of Significant Accoun25

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation — The accompanying consolidated financial statements include the accounts of all our wholly-owned subsidiaries and are prepared in accordance with accounting principles generally accepted in the United States of America. All inter-company accounts and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates — The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amount of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reported period. Our significant estimates include primarily those required in the valuation or impairment analysis of goodwill, property and equipment, revenue recognition, allowances for doubtful accounts, stock-based compensation, litigation accruals, valuation allowances for deferred tax assets and tax accruals. Although we believe that adequate accruals have been made for unsettled issues, additional gains or losses could occur in future years from resolutions of outstanding matters. Actual results could differ materially from original estimates.
Cash Equivalents	Cash Equivalents — Cash investments with maturities of three months or less when purchased are considered cash equivalents.
Fair Value of Financial Instruments	Fair Value of Financial Instruments —The Company does not measure the fair value of any financial instrument other than cash equivalents, options, and other equity awards. The carrying values of other financial instruments (receivables and accounts payable) are not recorded at fair value but approximate fair values primarily due to their short-term nature. The carrying values of other current assets and accrued expenses are also not recorded at fair value, but approximate fair values primarily due to their short-term nature.
Valuation of Property and Equipment	Valuation of Property and Equipment — The accounting policies and estimates relating to property and equipment are considered significant because of the potential impact that impairment, obsolescence, or change in an asset’s useful life could have on the Company’s operating results. We record an impairment charge on the assets to be held and used when we determine based upon certain triggering events that the carrying value of property and equipment may not be recoverable based on expected undiscounted cash flows attributable to such assets. The amount of a potential impairment is determined by comparing the carrying amount of the asset to either the value determined from a projected discounted cash flow method, using a discount rate that is considered to be commensurate with the risk inherent in the Company’s current business model or the estimated fair market value. Assumptions are made with respect to future net cash flows expected to be generated by the related asset. An impairment charge would be recorded for an amount by which the carrying value of the asset exceeded the discounted projected net cash flows or estimated fair market value. Also, even where a current impairment charge is not necessary, the remaining useful lives are evaluated. No impairment was recorded for any of the periods presented. Property and equipment are recorded at cost and depreciated or amortized using the straight-line method over their estimated useful lives as follows: computer and office equipment and software — three years; leasehold improvements — the shorter of five years or the lease term; and furniture and fixtures — five years.
Goodwill	Goodwill — We account for the valuation of goodwill and other intangible assets after classifying intangible assets into three categories: (1) intangible assets with finite lives subject to amortization; (2) intangible assets with indefinite lives not subject to amortization; and (3) goodwill. For intangible assets with finite lives, tests for impairment must be performed if conditions exist that indicate the carrying value may not be recoverable. For intangible assets with indefinite lives and goodwill, tests for impairment must be performed at least annually or more frequently if events or circumstances indicate that assets might be impaired. Goodwill was $2.2 million, or 2% and 3% of total assets for the years ended December 31, 2015 and 2014, respectively. Our goodwill is not being amortized, but we do evaluate the goodwill for impairment annually in the fourth quarter, or when there is reason to believe that the value has been diminished or impaired. Evaluations for possible impairment are based upon a comparison of the estimated fair value of the reporting unit to which the goodwill has been assigned, versus the sum of the carrying value of the assets and liabilities of that unit including the assigned goodwill value. The fair values used in this evaluation are estimated based on the Company’s market capitalization, which is based on the outstanding stock and market price of the stock. Impairment is deemed to exist if the net book value of the unit exceeds its estimated fair value. No impairment was recorded for any of the periods presented.
Deferred Tax Assets	Deferred Tax Assets — Deferred tax assets are recognized if it is “more likely than not” that the benefit of the deferred tax asset will be realized on future federal or state income tax returns. At December 31, 2015, we provided a valuation allowance against a significant portion, $ 46.1 million, of our accumulated U.S. deferred tax assets, reflecting our historical losses and the uncertainty of future taxable income sufficient to utilize net operating loss carryforwards prior to their expiration. Our total deferred tax asset not subject to a valuation allowance is valued at $48.9 million, and consists of $41.8 million for federal net operating loss carryforwards, $4.1 million relating to temporary timing differences between GAAP and tax-related expense, $1.8 million relating to U.S. state income tax credits and $1.2 million related to Alternative Minimum Tax credits. If U.S. taxable income increases from its current level in a future period or if the facts and circumstances on which our estimates and assumptions are based were to change, thereby impacting the likelihood of realizing the deferred tax assets, judgment would have to be applied in determining the amount of valuation allowance no longer required. Reversal of all or a part of this valuation allowance could have a significant positive impact on operating results in the period that it becomes more likely than not that certain of the Company’s deferred tax assets will be realized. Alternatively, should our future income decrease from current levels, a resulting increase to all or a part of this valuation allowance could also have a significant negative impact on our operating results.
Leases	Leases — A leased asset whose lease terms meet the criteria for capitalization is recorded as an asset and depreciated. If a lease does not meet the criteria for capitalization, it is classified as an operating lease and payments are recorded as rent expense. For 2015 and 2014 we had no leases that qualified as capital leases. Lease renewal options which we are “reasonably assured” of using and the related payments are taken into account when initially classifying and recording the lease as a capital lease obligation or as straight-line rent if an operating lease. Funds provided by the lessor for leasehold improvements are recorded as a deferred lease incentive and amortized as a reduction of rent expense over the lease term.
Revenue Recognition	Revenue Recognition — We develop, market, and support applications that connect, protect and deliver information in a secure manner. We generate our sales through both a direct sales team and, increasingly, through our channel partners. We derive our revenue from subscription fees for rights related to the use of our software. Software subscription terms typically range from one to three years. Revenue is recognized when all of the following criteria have been met: · persuasive evidence of an arrangement exists, · delivery has occurred or services have been rendered, · the price is fixed and determinable, and · collectability is probable. We record our revenue net of any value added or sales tax. Discounts provided to customers are recorded as reductions in revenue. We have determined that substantially all of our revenue arrangements are in the scope of the software revenue recognition rules. Multiple elements in our software arrangements are sold as a single unit consisting of the following elements: (i) subscription licensed software delivered to the customer’s site, (ii) ongoing customer support and, (iii) access to our hosted encryption network (Zix encryption network) during the term of the agreement. (i) Software at the customer site performs critical functions of the email encryption process and is the predominant element in our arrangements. Actions performed by the software at the customer site include identifying when encryption is needed through the use of filters and lexicons, determining the best method of delivery (BMOD) by examining secure connection options and selecting the BMOD. BMOD is a key marketing differentiator for us and is defined as the most secure and easiest method to deliver encrypted email. Customers can install the software on their own hardware or we can deliver to the customer site hardware that we own. In recent years more customers have opted to have the software installed on their own hardware, and as a result the number of Zix supplied hardware devices has declined. Any hardware provided as part of our services primarily included manufacturer provided warranty provisions. We recorded no warranty expense in any of the presented periods. ( ii ) Customer support includes unspecified software upgrades, updates and bug fixes and access to live technical support technicians and on-line knowledge resources ( ii i) The Zix encryption network includes access to our central network which facilitates transparent encrypted email exchange among all of our customers by providing public encryption keys (asymmetrical encryption requires two keys- a public key provided by the central network and a private key generated by the software at the customer site). The delivered software element is essential to the functionality and utility of this central network. The network also enables our customers to send encrypted emails to non-Zix customer recipients through a portal. A small portion of our revenue (less than 5% in 2015) is derived from hosted email encryption solutions. We apply general revenue recognition guidance to these hosted arrangements. In all revenue arrangements we cannot determine vendor specific objective evidence (VSOE) and we cannot establish separate units of accounting for the multiple elements of our arrangements that are bundled and sold as one unit. All revenue arrangements are sales of subscription based (i.e. time-based) licenses. We defer revenue until the software is delivered and the service is deployed. Upon deployment, we commence revenue recognition and revenue is recognized ratably over the subscription period generally ranging from one to three years.
Software Development Costs	Software Development Costs —Costs incurred in the development and testing of subscription software products related to research, project planning, training, maintenance and general and administrative activities, and overhead costs are expensed as incurred. The costs of relatively minor upgrades and enhancements to the software are also expensed as incurred. Costs for the development of new software solutions and substantial enhancements to existing software solutions are expensed as incurred until technological feasibility has been established, at which time any additional costs would be capitalized. No research and development costs have been capitalized because we believe that technological feasibility is established concurrent with general release to customers. Research and development costs associated with software developed for internal use on behalf of our customers are capitalized. To date, capitalized costs for software developed for internal use on behalf of our customers were not material.
Advertising Expense	Advertising Expense — Advertising costs are expensed as incurred. Our operations include advertising expense of $ 2.1 million, $2.9 million, and $959 thousand in 2015, 2014, and 2013, respectively.
Stock-Based Compensation	Stock-Based Compensation — We currently use the straight-line amortization method for recognizing stock option and restricted stock compensation costs. The measurement and recognition of compensation expense for all share-based payment awards made to our employees and directors are based on the estimated fair value of the awards on the grant dates. The grant date fair value is estimated using either an option-pricing model which is consistent with the terms of the award or a market observed price, if such a price exists. Such cost is recognized over the period during which an employee or director is required to provide service in exchange for the award, i.e., “the requisite service period” (which is usually the vesting period). We also estimate the number of instruments that will ultimately be earned, rather than accounting for forfeitures as they occur.
Earnings Per Share ("EPS")	Earnings Per Share (“EPS”) — Basic EPS is based on the weighted average number of common shares outstanding during each period. Diluted EPS adjusts Basic EPS for the effects of dilutive common stock equivalents outstanding during each period using the treasury stock method.
New Accounting Standards	New Accounting Standards Revenue Recognition In May 2014, the FASB issued Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (ASU 2014-09), which supersedes most current revenue recognition guidance under U.S. GAAP. The core principle of ASU 2014-09 is to recognize revenues when promised goods or services are transferred to customers in an amount that reflects the consideration to which an entity expects to be entitled for those goods or services. ASU 2014-09 defines a five step process to achieve this core principle and, in doing so, more judgment and estimates may be required within the revenue recognition process than are required under existing U.S. GAAP. The standard is effective for us beginning 2018, and requires using either of the following transition methods: (i) a full retrospective approach reflecting the application of the standard in each prior reporting period with the option to elect certain practical expedients, or (ii) a retrospective approach with the cumulative effect of initially adopting ASU 2014-09 recognized at the date of adoption (which includes additional footnote disclosures). We are currently evaluating the impact of our pending adoption of ASU 2014-09 on our consolidated financial statements and have not yet determined the method by which we will adopt the standard in 2018. Classification of Deferred Taxes In November 2015, the FASB issued guidance that requires entities to present deferred tax assets and deferred tax liabilities as noncurrent on the balance sheet. The standard will be effective for annual periods beginning after December 15, 2016, but may be adopted early. This new guidance did not have a material impact on our consolidated financial statements. We have chosen to prospectively apply the guidance to our 2015 balance sheet. Prior year balances were not retroactively adjusted.

Stock Options and Stock-based26

Stock Options and Stock-based Employee Compensation (Tables)	12 Months Ended
	Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Common Stock Options	Below is a summary of common stock options outstanding at December 31, 2015: Authorized Shares Options Outstanding Options Vested Available for Grant Employee and Director Stock Option Plans: 2001 Stock Option Plan 2,525,000 11,400 11,400 — 2001 Employee Stock Option Plan 300,000 4,020 4,020 — 2004 Stock Option Plan 5,000,000 1,258,069 1,258,069 — 2006 Director’s Stock Option Plan 1,100,000 209,500 209,500 — 2012 Incentive Plan 6,300,000 291,563 153,249 3,751,308 Total 15,225,000 1,774,552 1,636,238 3,751,308
Summary of Stock-Based Employee Compensation Expense	For the twelve months ended December 31, 2015, 2014, and 2013, respectively, the total stock-based compensation expense resulting from stock options, RSAs, RSUs, and PUs was recorded to the following line items of our consolidated statements of income: Year Ended December 31, (In thousands) 2015 2014 2013 Cost of revenue $ 182 $ 180 $ 172 Research and development expenses 242 237 212 Selling, general and administrative expenses 1,749 1,264 1,327 Stock-based compensation expense $ 2,173 $ 1,681 $ 1,711
Schedule of Fair Value Option Award	The following weighted average assumptions were applied in determining the fair value of options granted during the respective periods: Year Ended December 31, 2015 2014 2013 Risk-free interest rate — — 1.05 % Expected option life (years) — — 5.8 Expected stock price volatility — — 69 % Expected dividend yield — — — Fair value of options granted — — $ 1.99
Summary of All Stock Option Transactions	The following is a summary of all stock option transactions for the three years ended December 31, 2015: Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Yrs) Outstanding at January 1, 2013 7,684,776 $ 4.28 Granted at market price 150,000 $ 3.27 Cancelled or expired (247,139 ) $ 5.15 Exercised (839,263 ) $ 2.03 Outstanding at December 31, 2013 6,748,374 $ 4.50 Granted at market price — — Cancelled or expired (1,850,036 ) $ 7.71 Exercised (407,829 ) $ 1.83 Outstanding at December 31, 2014 4,490,509 $ 3.42 Granted at market price — — Cancelled or expired (47,029 ) $ 4.69 Exercised (2,668,928 ) $ 3.25 Outstanding at December 31, 2015 1,774,552 $ 3.65 3.41 Options exercisable at December 31, 2015 1,636,238 $ 3.73 3.13
Summarized Information about Stock Options Outstanding by Range of Exercise Prices	Summarized information about stock options outstanding at December 31, 2015, is as follows: Options Outstanding Options Exercisable Range of Exercise Prices Number Outstanding Weighted Average Remaining Contractual Life Weighted Average Exercise Price Number Exercisable Weighted Average Exercise Price $1.11 - $1.99 204,050 2.15 $ 1.41 204,050 $ 1.41 $2.00 - $3.49 567,142 5.61 $ 2.59 428,828 $ 2.54 $3.50 - $4.99 1,003,360 2.37 $ 4.71 1,003,360 $ 4.71 1,774,552 3.41 $ 3.65 1,636,238 $ 3.73
Summary of All Restricted Stock Activity	The following is a summary of all restricted stock activity during the three years ended December 31, 2015: Restricted Shares Weighted Average Fair Value Non-vested at January 1, 2013 351,000 $ 2.49 Granted at market price 385,000 $ 3.45 Vested (87,750 ) $ 2.49 Cancelled — — Non-vested restricted stock at December 31, 2013 648,250 $ 3.06 Granted at market price 140,000 $ 4.66 Vested (184,000 ) $ 2.99 Cancelled — — Non-vested restricted stock at December 31, 2014 604,250 $ 3.45 Granted at market price 100,000 $ 5.18 Vested (240,750 ) $ 3.35 Cancelled (40,250 ) $ 3.57 Non-vested restricted stock at December 31, 2015 423,250 $ 3.91
Summary of All Restricted Stock Unit Activity	The following is a summary of all RSU activity during the three years ended December 31, 2015: Restricted Stock Units Weighted Average Fair Value Non-vested at January 1, 2013 113,000 $ 2.49 Granted at market price 95,000 $ 3.45 Vested (28,250 ) $ 2.49 Cancelled — — Non-vested restricted stock units at December 31, 2013 179,750 $ 3.00 Granted at market price 55,000 $ 4.66 Vested (52,000 ) $ 2.93 Cancelled — — Non-vested restricted stock units at December 31, 2014 182,750 $ 3.52 Granted at market price 215,000 $ 3.88 Vested (65,750 ) $ 3.29 Cancelled (32,500 ) $ 3.88 Non-vested restricted stock units at December 31, 2015 299,500 $ 3.79
Summary of All Performance Unit Activity	The following is a summary of all PU activity during the two years ended December 31, 2015: Restricted Stock Units Weighted Average Fair Value Non-vested at January 1, 2014 — — Granted at market price 100,000 $ 4.66 Vested — — Forfeited (100,000 ) $ 4.66 Non-vested restricted stock units at December 31, 2014 — — Granted at market price 215,000 $ 3.88 Vested — — Forfeited (32,500 ) $ 3.88 Non-vested restricted stock units at December 31, 2015 182,500 $ 3.88

Supplemental Cash Flow Inform27

Supplemental Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2015
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information Relating to Taxes and Non-Cash Activities	Supplemental information relating to taxes and noncash activities: Year Ended December 31, (In thousands) 2015 2014 2013 Income tax payments $ 332 $ 426 $ 217 Payables related to purchases of capitalized assets $ 55 $ (12 ) $ (97 ) Excess tax benefit on exercise and vesting of employee equity awards $ 103 $ 168 $ 427

Receivables, Net (Tables)

Receivables, Net (Tables)	12 Months Ended
	Dec. 31, 2015
Receivables [Abstract]
Summary of Net Receivables	(In thousands) December 31, 2015 2014 Gross accounts receivables $ 7,882 $ 8,116 Allowance for returns and doubtful accounts (59 ) (108 ) Unpaid portion of deferred revenue (7,325 ) (6,556 ) Note receivable 458 458 Allowance for note receivable (458 ) (458 ) Receivables, net $ 498 $ 1,452

Prepaid and other current ass29

Prepaid and other current assets (Tables)	12 Months Ended
	Dec. 31, 2015
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Schedule of Prepaid and Other Current Assets	(In thousands) December 31, 2015 2014 Prepaid insurance, maintenance, software licenses and other $ 2,596 $ 1,954 Deferred commissions 364 443 Tax-related (52 ) (25 ) Prepaid and other current assets $ 2,908 $ 2,372

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2015
Property Plant And Equipment [Abstract]
Summary of Property and Equipment	(In thousands) December 31, 2015 2014 Computer and office equipment and software $ 23,797 $ 23,013 Leasehold improvements 6,663 6,398 Furniture and fixtures 1,969 1,916 32,429 31,327 Less accumulated depreciation and amortization (28,286 ) (26,928 ) Total Property and Equipment $ 4,143 $ 4,399

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2015
Payables And Accruals [Abstract]
Summary of Accrued Expenses	December 31, (In thousands) 2015 2014 Employee compensation and benefits $ 3,028 $ 1,061 Professional fees 467 473 Taxes 399 378 Other 803 1,018 Total accrued expenses $ 4,697 $ 2,930

Earnings Per Share and Potent32

Earnings Per Share and Potential Dilution (Tables)	12 Months Ended
	Dec. 31, 2015
Earnings Per Share [Abstract]
Computations of Basic and Diluted Earnings Per Share	The computations for basic and diluted earnings per share for the years ended December 31, 2015, 2014, and 2013, are as follows: Year Ended December 31, 2015 2014 2013 Basic weighted average shares 56,421,833 57,948,864 61,139,035 Effect of dilutive securities: Employee and director stock options 741,002 782,659 1,095,227 Restricted Stock 172,126 181,219 225,741 RSUs 100,353 53,832 66,504 PUs 40,692 51 — Potential dilutive common shares 57,476,006 58,966,625 62,526,507

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2015
Commitments And Contingencies Disclosure [Abstract]
Summary of Fixed Contractual Obligations and Commitments	A summary of our fixed contractual obligations and commitments at December 31, 2015, is as follows: (In thousands) 2016 2017 2018 2019 2020 Thereafter Total Operating leases $ 1,369 $ 1,131 $ 1,027 $ 1,030 $ 1,035 $ 4,125 $ 9,717

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Components of Income Taxes	Components of the income taxes are as follows: (In thousands) 2015 2014 2013 Current: U.S. $ 58 $ 67 $ 124 State 196 240 148 Foreign 146 125 123 Deferred Federal 2,744 2,396 (1,400 ) State — — — Foreign — 2 (1 ) Income tax expense (benefit) $ 3,144 $ 2,830 $ (1,006 )
Schedule of Reconciliation of Tax Expense Benefit to Income Taxes	A reconciliation of the expected U.S. tax expense (benefit) to income taxes is as follows: (In thousands) 2015 2014 2013 Expected tax (benefit) expense at U.S. statutory rate $ 2,775 $ 2,357 $ 3,212 Decrease in valuations allowance- Operations — — (2,650 ) Decrease in valuations allowance- Other — — (1,400 ) Nondeductible expense and nontaxable income 133 127 (370 ) State income taxes 129 224 98 Foreign income taxes 146 127 122 Other (39 ) (5 ) (18 ) Income tax expense (benefit) $ 3,144 $ 2,830 $ (1,006 )
Components of Deferred Income Taxes	Components of our U.S. deferred income taxes as of December 31, 2015 and 2014 are as follows: (In thousands) 2015 2014 Deferred tax assets: Reserves- Other $ 156 $ 325 U.S. net operating loss carryforwards 84,591 86,382 State net operating loss carryforwards 281 281 Tax credit carryforwards 6,030 5,863 Stock-based compensation 1,767 2,623 Intangible assets 98 538 Depreciable assets 1,518 1,461 Other assets 1,272 712 Total deferred tax assets 95,713 98,185 Deferred tax liabilities: Prepaid expenses (671 ) (496 ) Total deferred tax assets 95,042 97,689 Less valuation allowance (46,134 ) (46,038 ) Net deferred tax assets $ 48,908 $ 51,651

Quarterly Results of Operatio35

Quarterly Results of Operations (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Summary of Quarterly Results of Operations	The following is a summary of the quarterly results of operations for the years ended December 31, 2015 and 2014: Quarter Ended (In thousands except per share data) March 31 June 30 September 30 December 31 2015 Revenues $ 13,073 $ 13,302 $ 14,011 $ 14,327 Gross margin 10,860 10,873 11,582 11,805 Net income 1,176 1,115 1,927 798 Basic net income per common share* 0.02 0.02 0.03 0.01 Diluted net income per common share* 0.02 0.02 0.03 0.01 2014 Revenues $ 12,162 $ 12,615 $ 12,705 $ 12,865 Gross margin 10,137 10,583 10,643 10,660 Net income 1,059 977 1,163 904 Basic net income per common share* 0.02 0.02 0.02 0.02 Diluted net income per common share* 0.02 0.02 0.02 0.02 * Net income per share is calculated independently for each quarter. The sum of Net income per share for each quarter may not equal the total Net income per share for the year due to rounding differences.

Summary of Significant Accoun36

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Significant Accounting Policies [Line Items]
Cash investments maturities	3 months
Goodwill	$ 2,161,000	$ 2,161,000
Goodwill to total asset	2.00%	3.00%
Impairment	$ 0
Accumulated deferred tax assets	46,134,000	$ 46,038,000
Total deferred tax asset not subject to a valuation allowance	48,908,000	51,651,000
Temporary timing differences between GAAP and tax-related expense	4,100,000
Income tax credits	6,030,000	5,863,000
Alternative Minimum Tax credits	1,200,000
Warranty expense	0	0	$ 0
Research and development expenses	8,317,000	9,051,000	9,563,000
Advertising expense	$ 2,100,000	$ 2,900,000	$ 959,000
Minimum [Member]
Schedule Of Significant Accounting Policies [Line Items]
Software subscription term	1 year
Maximum [Member]
Schedule Of Significant Accounting Policies [Line Items]
Software subscription term	3 years
Maximum [Member] | Customer Concentration Risk [Member] | Sales Revenue Net [Member]
Schedule Of Significant Accounting Policies [Line Items]
Portion of revenue in percentage	5.00%
Federal [Member]
Schedule Of Significant Accounting Policies [Line Items]
Federal net operating loss carryforwards	$ 41,800,000
State [Member]
Schedule Of Significant Accounting Policies [Line Items]
Income tax credits	$ 1,800,000
Computer and Office Equipment [Member]
Schedule Of Significant Accounting Policies [Line Items]
Estimated useful lives of depreciated or amortized Property and equipment	3 years
Office Equipment [Member]
Schedule Of Significant Accounting Policies [Line Items]
Estimated useful lives of depreciated or amortized Property and equipment	3 years
Software [Member]
Schedule Of Significant Accounting Policies [Line Items]
Estimated useful lives of depreciated or amortized Property and equipment	3 years
Research and development expenses	$ 0
Leasehold Improvements [Member]
Schedule Of Significant Accounting Policies [Line Items]
Estimated useful lives of depreciated or amortized Property and equipment	5 years
Furniture and Fixtures [Member]
Schedule Of Significant Accounting Policies [Line Items]
Estimated useful lives of depreciated or amortized Property and equipment	5 years

Stock Options and Stock-based37

Stock Options and Stock-based Employee Compensation - Summary of Common Stock Options (Detail) - shares	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized Shares	15,225,000
Options Outstanding	1,774,552	4,490,509	6,748,374	7,684,776
Options Vested	1,636,238
Shares Available for Grant	3,751,308
2001 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized Shares	2,525,000
Options Outstanding	11,400
Options Vested	11,400
2001 Employee Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized Shares	300,000
Options Outstanding	4,020
Options Vested	4,020
2004 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized Shares	5,000,000
Options Outstanding	1,258,069
Options Vested	1,258,069
2006 Director's Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized Shares	1,100,000
Options Outstanding	209,500
Options Vested	209,500
2012 Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized Shares	6,300,000
Options Outstanding	291,563
Options Vested	153,249
Shares Available for Grant	3,751,308

Stock Options and Stock-based38

Stock Options and Stock-based Employee Compensation - Additional Information (Detail) - USD ($) $ in Thousands	Jun. 24, 2015	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiry of option			10 years
Vesting period of options			3 years
Shares available for issuance			15,225,000
Additional shares underlying options outstanding	3,600,000
Total unrecognized stock-based compensation related to non-vested stock-based compensation awards			$ 2,100
The number of years over which cost is expected to be recognized			1 year 6 months
Stock-based compensation expense			$ 2,173	$ 1,681	$ 1,711
Deferred tax assets, tax deferred expense compensation and benefits employee compensation			$ 625	$ 462	$ 483
Options granted during period			0	0	150,000
Stock option exercised			2,668,928	407,829	839,263
Excess tax benefit on exercise of employee stock options			$ 19
Options Outstanding			1,774,552	4,490,509	6,748,374	7,684,776
Options, options exercisable			1,636,238
Number Exercisable			1,636,238	4,135,731	5,908,498
Tax benefit from RSA's vested			$ 84
Scenario Forecast [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance unit vesting in period		27,428
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value of options exercised			$ 4,400	$ 716
Employee and Director Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Outstanding			1,774,552	2,207,201
Options, options exercisable			1,636,238	1,852,423
Aggregate intrinsic value of options outstanding			$ 2,500	$ 2,400
Aggregate intrinsic value of options exercisable			2,200	$ 2,100
CEO [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			$ 540
CEO [Member] | Scenario Forecast [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance unit vesting in period		10,350
2012 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of options			4 years
Shares available for issuance			2,700,000
Additional shares underlying options outstanding			1,327,000

Stock Options and Stock-based39

Stock Options and Stock-based Employee Compensation - Summary of Stock-Based Employee Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 2,173	$ 1,681	$ 1,711
Cost of Revenue [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	182	180	172
Research and Development Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	242	237	212
Selling, General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 1,749	$ 1,264	$ 1,327

Stock Options and Stock based E

Stock Options and Stock based Employee Compensation - Schedule of Fair Value Option Award (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rate			1.05%
Expected option life (years)	0 years	0 years	5 years 9 months 18 days
Expected stock price volatility			69.00%
Expected dividend yield	0.00%	0.00%	0.00%
Fair value of options granted			$ 1.99

Stock Options and Stock-based41

Stock Options and Stock-based Employee Compensation - Summary of All Stock Option Transactions (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward
Shares, Outstanding, Beginning Balance	4,490,509	6,748,374	7,684,776
Shares, Granted at market price	0	0	150,000
Shares, Cancelled or expired	(47,029)	(1,850,036)	(247,139)
Shares, Exercised	(2,668,928)	(407,829)	(839,263)
Shares, Outstanding Ending Balance	1,774,552	4,490,509	6,748,374
Shares, Options Exercisable	1,636,238
Weighted Average Exercise Price, Outstanding, Beginning Balance	$ 3.42	$ 4.50	$ 4.28
Weighted Average Exercise Price, Granted at market price			3.27
Weighted Average Exercise Price, Cancelled or expired	4.69	7.71	5.15
Weighted Average Exercise Price, Exercised	3.25	1.83	2.03
Weighted Average Exercise Price, Outstanding, Ending Balance	3.65	$ 3.42	$ 4.50
Weighted Average Exercise Price, Options Exercisable	$ 3.73
Weighted Average Remaining Contractual Term, Outstanding	3 years 4 months 28 days
Weighted Average Remaining Contractual Term, Options exercisable	3 years 1 month 17 days

Stock Options and Stock-based42

Stock Options and Stock-based Employee Compensation - Summarized Information about Stock Options Outstanding by Range of Exercise Prices (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule Of Stock Options [Line Items]
Number Outstanding	1,774,552	4,490,509	6,748,374	7,684,776
Weighted Average Remaining Contractual Life, Options Outstanding	3 years 4 months 28 days
Weighted Average Exercise Price, Options Outstanding	$ 3.65
Number Exercisable	1,636,238	4,135,731	5,908,498
Weighted Average Exercise Price, Options Exercisable	$ 3.73
$ 1.11 - $ 1.99 [Member]
Schedule Of Stock Options [Line Items]
Range of Exercise Prices, Lower range	1.11
Range of Exercise Prices, Upper range	$ 1.99
Number Outstanding	204,050
Weighted Average Remaining Contractual Life, Options Outstanding	2 years 1 month 24 days
Weighted Average Exercise Price, Options Outstanding	$ 1.41
Number Exercisable	204,050
Weighted Average Exercise Price, Options Exercisable	$ 1.41
$ 2.00 - $ 3.49 [Member]
Schedule Of Stock Options [Line Items]
Range of Exercise Prices, Lower range	2
Range of Exercise Prices, Upper range	$ 3.49
Number Outstanding	567,142
Weighted Average Remaining Contractual Life, Options Outstanding	5 years 7 months 10 days
Weighted Average Exercise Price, Options Outstanding	$ 2.59
Number Exercisable	428,828
Weighted Average Exercise Price, Options Exercisable	$ 2.54
$ 3.50 - $ 4.99 [Member]
Schedule Of Stock Options [Line Items]
Range of Exercise Prices, Lower range	3.50
Range of Exercise Prices, Upper range	$ 4.99
Number Outstanding	1,003,360
Weighted Average Remaining Contractual Life, Options Outstanding	2 years 4 months 13 days
Weighted Average Exercise Price, Options Outstanding	$ 4.71
Number Exercisable	1,003,360
Weighted Average Exercise Price, Options Exercisable	$ 4.71

Stock Options and Stock-Based43

Stock Options and Stock-Based Employee Compensation Expense - Summary of All Restricted Stock Activity (Detail) - Restricted Stock [Member] - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Non-vested, Beginning balance | shares	604,250	648,250	351,000
Shares, Granted at market price | shares	100,000	140,000	385,000
Shares, Vested | shares	(240,750)	(184,000)	(87,750)
Shares, Cancelled | shares	(40,250)
Shares, Non-vested, Ending balance | shares	423,250	604,250	648,250
Weighted Average Fair Value, Non-vested, Beginning balance	$ 3.45	$ 3.06	$ 2.49
Weighted Average Fair Value, Granted at market price	5.18	4.66	3.45
Weighted Average Fair Value, Vested	3.35	2.99	2.49
Weighted Average Fair Value, Cancelled	3.57	0	0
Weighted Average Fair Value, Non-vested, Ending balance	$ 3.91	$ 3.45	$ 3.06

Stock Options and Stock-based44

Stock Options and Stock-based Employee Compensation - Summary of All Restricted Stock Unit Activity (Detail) - Restricted Stock Units (RSUs) [Member] - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Non-vested, Beginning balance | shares	182,750	179,750	113,000
Shares, Granted at market price | shares	215,000	55,000	95,000
Shares, Vested | shares	(65,750)	(52,000)	(28,250)
Shares, Cancelled | shares	(32,500)
Shares, Non-vested, Ending balance | shares	299,500	182,750	179,750
Weighted Average Fair Value, Non-vested, Beginning balance	$ 3.52	$ 3	$ 2.49
Weighted Average Fair Value, Granted at market price	3.88	4.66	3.45
Weighted Average Fair Value, Vested	3.29	2.93	2.49
Weighted Average Fair Value, Cancelled	3.88	0	0
Weighted Average Fair Value, Non-vested, Ending balance	$ 3.79	$ 3.52	$ 3

Stock Options and Stock-based45

Stock Options and Stock-based Employee Compensation - Summary of Performance Unit Activity (Detail) - Performance Units [Member] - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Non-vested, Beginning balance | shares	0	0
Shares, Granted at market price | shares	215,000	100,000
Shares, Cancelled | shares	(32,500)	(100,000)
Shares, Non-vested, Ending balance | shares	182,500	0
Weighted Average Fair Value, Non-vested, Beginning balance	$ 0	$ 0
Weighted Average Fair Value, Granted at market price	3.88	4.66
Weighted Average Fair Value, Vested		0
Weighted Average Fair Value, Cancelled	3.88	4.66
Weighted Average Fair Value, Non-vested, Ending balance	$ 3.88	$ 0

Supplemental Cash Flow Inform46

Supplemental Cash Flow Information - Supplemental Cash Flow Information Relating to Taxes and Non-Cash Activities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Additional Cash Flow Elements And Supplemental Cash Flow Information [Abstract]
Income tax payments	$ 332	$ 426	$ 217
Payables related to purchases of capitalized assets	55	(12)	(97)
Excess tax benefit on exercise and vesting of employee equity awards	$ 103	$ 168	$ 427

Receivables, Net - Summary of N

Receivables, Net - Summary of Net Receivables (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Accounts Notes And Loans Receivable Net Current [Abstract]
Gross accounts receivables	$ 7,882	$ 8,116
Allowance for returns and doubtful accounts	(59)	(108)
Unpaid portion of deferred revenue	(7,325)	(6,556)
Note receivable	458	458
Allowance for note receivable	(458)	(458)
Receivables, net	$ 498	$ 1,452

Receivables, Net - Additional I

Receivables, Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivables	$ 7,882	$ 8,116
Percentage of doubtful debts on accounts receivable	2.50%
Note receivable on a product line	$ 540
Date of note receivable, reserved	Dec. 31, 2015
Tenant Improvement Allowance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivables	$ 318

Prepaid and Other Current Ass49

Prepaid and Other Current Assets - Schedule of Prepaid and Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Prepaid Expense And Other Assets Current [Abstract]
Prepaid insurance, maintenance, software licenses and other	$ 2,596	$ 1,954
Deferred commissions	364	443
Tax-related	(52)	(25)
Prepaid and other current assets	$ 2,908	$ 2,372

Property and Equipment - Summar

Property and Equipment - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property and equipment gross	$ 32,429	$ 31,327
Less accumulated depreciation and amortization	(28,286)	(26,928)
Total Property and Equipment	4,143	4,399
Computer and Office Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	23,797	23,013
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	6,663	6,398
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	$ 1,969	$ 1,916

Property and Equipment - Additi

Property and Equipment - Additional information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property Plant And Equipment [Abstract]
Depreciation and amortization	$ 2,152	$ 1,623	$ 1,466

Goodwill - Additional Informati

Goodwill - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill	$ 2,161,000	$ 2,161,000
Goodwill impairment	$ 0

Accrued Expenses - Summary of A

Accrued Expenses - Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Accounts Payable And Accrued Liabilities Current [Abstract]
Employee compensation and benefits	$ 3,028	$ 1,061
Professional fees	467	473
Taxes	399	378
Other	803	1,018
Total accrued expenses	$ 4,697	$ 2,930

Earnings Per Share and Potent54

Earnings Per Share and Potential Dilution - Computations of Basic and Diluted Earnings Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Weighted Average Number of Shares [Line Items]
Basic weighted average shares	56,421,833	57,948,864	61,139,035
Potential dilutive common shares	57,476,006	58,966,625	62,526,507
Employee and Director Stock Options [Member]
Weighted Average Number of Shares [Line Items]
Effect of dilutive securities	741,002	782,659	1,095,227
Restricted Stock [Member]
Weighted Average Number of Shares [Line Items]
Effect of dilutive securities	172,126	181,219	225,741
Restricted Stock Units (RSUs) [Member]
Weighted Average Number of Shares [Line Items]
Effect of dilutive securities	100,353	53,832	66,504
Performance Units [Member]
Weighted Average Number of Shares [Line Items]
Effect of dilutive securities	40,692	51

Earnings Per Share and Potent55

Earnings Per Share and Potential Dilution - Additional Information (Detail) - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Employee and Director Stock Options [Member]
Weighted Average Number of Shares [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	1,005,328	3,240,594	4,054,261
Restricted Stock [Member]
Weighted Average Number of Shares [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	56,542	147,292	31,281
Restricted Stock Units (RSUs) [Member]
Weighted Average Number of Shares [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	33,512	50,833	7,719
Performance Units [Member]
Weighted Average Number of Shares [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	24,486	33,333

Significant Customers - Additio

Significant Customers - Additional Information (Detail) - Customer	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Related Party Transactions [Abstract]
Customer accounted for revenue	0	0	0

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Commitments And Contingencies Disclosure [Abstract]
Rental expense on operating lease	$ 1.4	$ 1.4	$ 1.3
Operating leases, expiration year	2,024

Commitments and Contingencies58

Commitments and Contingencies - Summary of Fixed Contractual Obligations and Commitments (Detail) $ in Thousands	Dec. 31, 2015USD ($)
Operating Leases Future Minimum Payments Due [Abstract]
2,016	$ 1,369
2,017	1,131
2,018	1,027
2,019	1,030
2,020	1,035
Thereafter	4,125
Total	$ 9,717

Income Taxes - Components of In

Income Taxes - Components of Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current:
U.S.	$ 58	$ 67	$ 124
State	196	240	148
Foreign	146	125	123
Deferred
Federal	2,744	2,396	(1,400)
State	0	0	0
Foreign		2	(1)
Income tax expense (benefit)	$ 3,144	$ 2,830	$ (1,006)

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Tax Expense Benefit to Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Expected tax (benefit) expense at U.S. statutory rate	$ 2,775	$ 2,357	$ 3,212
Decrease in valuations allowance- Operations		0	(2,650)
Decrease in valuations allowance- Other		0	(1,400)
Nondeductible expense and nontaxable income	133	127	(370)
State income taxes	129	224	98
Foreign income taxes	146	127	122
Other	(39)	(5)	(18)
Income tax expense (benefit)	$ 3,144	$ 2,830	$ (1,006)

Income Taxes - Components of De

Income Taxes - Components of Deferred Income Taxes (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Reserves- Other	$ 156	$ 325
U.S. net operating loss carryforwards	84,591	86,382
State net operating loss carryforwards	281	281
Tax credit carryforwards	6,030	5,863
Stock-based compensation	1,767	2,623
Intangible assets	98	538
Depreciable assets	1,518	1,461
Other assets	1,272	712
Total deferred tax assets	95,713	98,185
Deferred tax liabilities:
Prepaid expenses	(671)	(496)
Total deferred tax assets	95,042	97,689
Less valuation allowance	(46,134)	(46,038)
Net deferred tax assets	$ 48,908	$ 51,651

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2013	Dec. 31, 2014
Income Taxes [Line Items]
Operating loss carryforwards	$ 84,591		$ 86,382
Change valuation allowance related to deferred tax assets		$ 4,100
Unrecognized tax benefits to significantly increase or decrease	12 months
Statute of limitations by major tax jurisdictions	3 years
Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Operating loss carryforwards	$ 249,000
U.S. net operating loss carryforwards expire	2,020
State [Member]
Income Taxes [Line Items]
Federal tax expense net/tax credit carryforwards	$ 1,700
Operating loss carryforwards, expiration dates	2,027
General Business Tax Credit Carry Forward [Member]
Income Taxes [Line Items]
Federal tax expense net/tax credit carryforwards	$ 4,300
Tax credit carry forward began to expiration	2,016

Employee Benefit Plan - Additio

Employee Benefit Plan - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Compensation And Retirement Disclosure [Abstract]
Net contribution from operations to employee benefit plan	$ 389	$ 354	$ 297

ZixCorp Repurchase Program - Ad

ZixCorp Repurchase Program - Additional Information (Detail) - USD ($)	May. 11, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	May. 31, 2015	Jul. 30, 2014	Nov. 06, 2013
Equity, Class of Treasury Stock [Line Items]
Shares repurchased		3,185,340	4,070,195	1,976,900
Treasury repurchase program		$ 15,000,000	$ 16,239,000	$ 8,760,000
Share repurchase program authorized amount						$ 10,000,000	$ 15,000,000
January 6, 2015 Stock Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Shares repurchased	0
Share repurchase program authorized amount	$ 10,000,000
Maximum [Member]
Equity, Class of Treasury Stock [Line Items]
Share repurchase program authorized amount					$ 15,000,000

Quarterly Results of Operatio65

Quarterly Results of Operations (Unaudited) - Summary of Quarterly Results of Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 14,327	$ 14,011	$ 13,302	$ 13,073	$ 12,865	$ 12,705	$ 12,615	$ 12,162	$ 54,713	$ 50,347	$ 48,138
Gross margin	11,805	11,582	10,873	10,860	10,660	10,643	10,583	10,137	45,120	42,023	40,524
Net income	$ 798	$ 1,927	$ 1,115	$ 1,176	$ 904	$ 1,163	$ 977	$ 1,059	$ 5,016	$ 4,103	$ 10,453
Basic net income per common share	$ 0.01	$ 0.03	$ 0.02	$ 0.02	$ 0.02	$ 0.02	$ 0.02	$ 0.02	$ 0.09	$ 0.07	$ 0.17
Diluted net income per common share	$ 0.01	$ 0.03	$ 0.02	$ 0.02	$ 0.02	$ 0.02	$ 0.02	$ 0.02	$ 0.09	$ 0.07	$ 0.17

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail)	Jan. 19, 2016Director	Jan. 05, 2016USD ($)	Dec. 31, 2015Director	Jul. 30, 2014USD ($)	Nov. 06, 2013USD ($)
Subsequent Event [Line Items]
Share repurchase program authorized amount | $				$ 10,000,000	$ 15,000,000
Number of board members | Director			5
Directors term expiration year			2,016
Subsequent Event [Member]
Subsequent Event [Line Items]
Share repurchase program authorized amount | $		$ 15,000,000
Share Repurchase Program expiration date		Sep. 30, 2016
Number of board members | Director	6