Zix (ZIXI) 10-Q 9 May 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	May 07, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	ZIXI
Entity Registrant Name	ZIX CORP
Entity Central Index Key	0000855612
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		55,547,299

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 16,691	$ 27,109
Receivables, net	9,779	3,188
Prepaid and other current assets	5,253	3,176
Total current assets	31,723	33,473
Property and equipment, net	7,000	3,924
Operating lease assets	8,932
Intangible assets, net	152,012	15,251
Goodwill	161,003	13,783
Deferred tax assets	29,888	28,785
Deferred costs and other assets	10,174	9,424
Total assets	400,732	104,640
Current liabilities:
Accounts payable	14,118	769
Accrued expenses	14,477	9,747
Deferred revenue	40,966	30,622
Current portion of long-term debt	1,765
Other current liabilities	1,203
Total current liabilities	72,529	41,138
Long-term liabilities:
Deferred revenue	1,304	1,539
Deferred rent		1,016
Noncurrent operating lease liabilities	8,880
Long-term debt	166,901
Total long-term liabilities	177,085	2,555
Total liabilities	249,614	43,693
Commitments and contingencies (see Note 11)
Preferred stock:
Convertible preferred stock	98,976
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; 83,288,103 issued and 55,596,180 outstanding in 2019 and 81,715,330 issued and 54,186,180 outstanding in 2018	779	779
Additional paid-in capital	386,205	384,940
Treasury stock, at cost; 27,691,923 common shares in 2019 and 27,529,150 common shares in 2018	(109,732)	(108,392)
Accumulated deficit	(225,062)	(216,364)
Accumulated other comprehensive loss	(48)	(16)
Total stockholders’ equity	52,142	60,947
Total liabilities, preferred stock and stockholders’ equity	400,732	$ 104,640
Series A Convertible Preferred Stock [Member]
Preferred stock:
Convertible preferred stock	64,644
Series B Convertible Preferred Stock [Member]
Preferred stock:
Convertible preferred stock	$ 34,332

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2019	Dec. 31, 2018
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	83,288,103	81,715,330
Common stock, shares outstanding	55,596,180	54,186,180
Treasury stock, shares	27,691,923	27,529,150
Series A Convertible Preferred Stock [Member]
Convertible Preferred stock, par value	$ 1	$ 1
Convertible Preferred stock, shares designated	64,914	0
Convertible Preferred stock, shares issued	64,914	0
Convertible Preferred stock, shares outstanding	64,914	0
Series B Convertible Preferred Stock [Member]
Convertible Preferred stock, par value	$ 1	$ 1
Convertible Preferred stock, shares designated	35,086	0
Convertible Preferred stock, shares issued	35,086	0
Convertible Preferred stock, shares outstanding	35,086	0

Condensed Consolidated Statemen

Condensed Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Revenue	$ 29,300	$ 16,654
Cost of revenue	11,139	3,514
Gross margin	18,161	13,140
Operating expenses:
Research and development	4,147	2,977
Selling, general and administrative	20,264	7,554
Total operating expenses	24,411	10,531
Operating (loss) income	(6,250)	2,609
Other income (expense):
Investment and other income	92	119
Interest expense	(1,255)
Total other (expense) income	(1,163)	119
Income (loss) before income taxes	(7,413)	2,728
Income tax benefit (expense)	1,148	(836)
Net income (loss)	(6,265)	1,892
Deemed and accrued dividends on preferred stock	2,433
Net income (loss) attributable to common stockholders	$ (8,698)	$ 1,892
Basic income (loss) per share attributable to common stockholders	$ (0.17)	$ 0.04
Diluted income (loss) per common share attributable to common stockholders	$ (0.17)	$ 0.04
Basic weighted average common shares outstanding	52,713,576	52,875,428
Diluted weighted average common shares outstanding	52,713,576	53,481,104
Other comprehensive income, net of tax
Foreign currency translation adjustments	$ (32)
Comprehensive income (loss)	$ (6,297)	$ 1,892

Condensed Consolidated Statem_2

Condensed Consolidated Statement of Preferred Stock and Stockholders’ Equity (Unaudited) - USD ($) $ in Thousands	Total	Series A Convertible Preferred Stock [Member]	Series B Convertible Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]Series A Convertible Preferred Stock [Member]	Preferred Stock [Member]Series B Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Treasury Stock [Member]	Accumulated Deficit [Member]	Accumulated Deficit [Member]Series A Convertible Preferred Stock [Member]	Accumulated Deficit [Member]Series B Convertible Preferred Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning balances at Dec. 31, 2017	$ 43,520						$ 778	$ 381,457	$ (102,343)	$ (236,372)
Beginning balances, shares at Dec. 31, 2017							80,709,970
Cumulative effect adjustment from changes in accounting standards, net of taxes at Dec. 31, 2017	4,564									4,564
Beginning balances, as adjusted at Dec. 31, 2017	48,084						$ 778	381,457	(102,343)	(231,808)
Net issuance of common stock upon vesting of restricted stock units, shares							50,751
Net issuance of common stock upon vesting of performance stock units, shares							32,655
Net issuance of restricted common stock, shares							370,322
Net issuance of restricted performance common stock, shares							95,946
Employee stock-based compensation costs	80							627	(547)
Treasury repurchase program	(3,090)								(3,090)
Net loss	1,892									1,892
Ending balances at Mar. 31, 2018	46,966						$ 778	382,084	(105,980)	(229,916)
Ending balances, shares at Mar. 31, 2018							81,259,644
Beginning balances at Dec. 31, 2018	60,947						$ 779	384,940	(108,392)	(216,364)			$ (16)
Beginning balances, shares at Dec. 31, 2018		0	0
Beginning balances, shares at Dec. 31, 2018							81,715,330
Issuance of preferred stock in connection with private placement					$ 62,662	$ 33,881
Issuance of preferred stock in connection with private placement, shares					64,914	35,086
Beneficial conversion feature of preferred stock		$ (1,407)			$ 1,407						$ (1,407)
Accretion of beneficial conversion feature of Preferred Shares (Participating)		(12)			12						(12)
Accrued dividend on preferred stock		$ (563)	$ (380)		$ 563	$ 380					$ (563)	$ (380)
Redemption Accretion of preferred stock			$ (71)			$ 71						$ (71)
Net issuance of common stock upon exercise of stock options	$ 36							36
Net issuance of common stock upon exercise of stock options, shares	17,438						17,438
Net issuance of common stock upon vesting of restricted stock units, shares							40,334
Net issuance of common stock upon vesting of performance stock units, shares							392,500
Net issuance of restricted common stock, shares							1,116,724
Net issuance of restricted performance common stock, shares							5,777
Employee stock-based compensation costs	$ (111)							1,229	(1,340)
Adjustment from foreign currency translation	(32)												(32)
Net loss	(6,265)									(6,265)
Ending balances at Mar. 31, 2019	52,142						$ 779	$ 386,205	$ (109,732)	$ (225,062)			$ (48)
Ending balances, shares at Mar. 31, 2019		64,914	35,086	100,000
Ending balances at Mar. 31, 2019	$ 98,976	$ 64,644	$ 34,332	$ 98,976
Ending balances, shares at Mar. 31, 2019							83,288,103

Condensed Consolidated Statem_3

Condensed Consolidated Statement of Preferred Stock and Stockholders’ Equity (Parenthetical) (Unaudited) - USD ($) $ in Thousands	Feb. 20, 2019	Mar. 31, 2019
Series A Convertible Preferred Stock [Member]
Preferred stock, net of issuance costs	$ 2,300	$ 2,253
Series B Convertible Preferred Stock [Member]
Preferred stock, net of issuance costs	$ 1,200	$ 1,204

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating activities:
Net income (loss)	$ (6,265)	$ 1,892
Non-cash items in net income (loss):
Depreciation and amortization	2,696	746
Amortization of debt issuance costs	116
Employee stock-based compensation costs	1,229	627
Changes in deferred taxes	(1,103)	912
Changes in operating assets and liabilities:
Receivables	(113)	275
Prepaid and other current assets	(1,004)	554
Deferred costs and other assets	(856)	(914)
Operating lease assets	(4,385)
Accounts payable	5,989	(295)
Deferred revenue	(212)	(1,586)
Earn-out payment	(385)	(195)
Accrued and other liabilities	3,876	(968)
Net cash provided by (used in) operating activities	(417)	1,048
Investing activities:
Purchases of property, equipment and internal-use software	(1,742)	(546)
Acquisition of business, net of cash acquired	(271,706)
Net cash used in investing activities	(273,448)	(546)
Financing activities:
Proceeds of term loan	175,000
Debt issuance cost	(6,389)
Proceeds from exercise of stock options	36
Purchase of treasury shares	(1,340)	(3,637)
Earn-out payment	(415)	(605)
Net cash provided by (used in) financing activities	263,480	(4,242)
Effect of exchange rate on cash	(33)
Decrease in cash and cash equivalents	(10,418)	(3,740)
Cash and cash equivalents, beginning of period	27,109	33,009
Cash and cash equivalents, end of period	16,691	$ 29,269
Series A Convertible Preferred Stock [Member]
Financing activities:
Proceeds from issuance of preferred stock, net of offering costs	62,692
Series B Convertible Preferred Stock [Member]
Financing activities:
Proceeds from issuance of preferred stock, net of offering costs	$ 33,896

Basis of Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Basis of Presentation	1. Basis of Presentation The accompanying condensed consolidated financial statements of Zix Corporation (“Zix” the “Company,” “we,” “our” or “us”) should be read in conjunction with the audited consolidated financial statements included in the Company’s 2018 Annual Report on Form 10-K. These financial statements are unaudited, but have been prepared in the ordinary course of business for the purpose of providing information with respect to the covered interim periods. Management of the Company believes that all adjustments necessary for a fair presentation for such periods have been included and are of a normal recurring nature. The results of operations for the three month period ended March 31, 2019, are not necessarily indicative of the results to be expected for any future periods or for the full fiscal year.

Recent Accounting Standards and

Recent Accounting Standards and Pronouncements	3 Months Ended
	Mar. 31, 2019
Accounting Changes And Error Corrections [Abstract]
Recent Accounting Standards and Pronouncements	2. Recent Accounting Standards and Pronouncements Leases In February 2016, the FASB issued Accounting Standards Update No. 2016-02, Leases (Topic 842). Topic 842 requires companies to generally recognize on the balance sheet operating and financing lease liabilities and corresponding right-of-use assets. We elected the available practical expedients and adopted ASC 842 effective January 1, 2019, prospectively. The adoption of this standard resulted in the recognition of right-to-use assets and lease liabilities of $4.8 million and $6.0 million, with no material impact on the results of operations and cash flows. See below Note 6 “Leases" for additional information regarding our leases.

Stock- Based Awards and Stock-B

Stock- Based Awards and Stock-Based Employee Compensation Expense	3 Months Ended
	Mar. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock- Based Awards and Stock-Based Employee Compensation Expense	3. Stock- Based Awards and Stock-Based Employee Compensation Expense Our stock-based awards include (i) stock options, (ii) restricted stock awards, some of which are subject to time-based vesting (“Restricted Stock”) and some of which are subject to performance-based vesting (“Performance Stock”), and (iii) restricted stock units, some of which are subject to time-based vesting (“RSUs”) and some of which are subject to performance-based vesting (“Performance RSUs”). As of March 31, 2019 the Company had 906,385 stock options outstanding, 2,090,603 non-vested Restricted Stock awards; 526,568 non-vested Performance Stock awards; 61,834 non-vested RSUs; 21,722 non-vested Performance RSUs and 4,320,776 shares of common stock available for grant. Stock Option Activity The following is a summary of all stock option transactions during the three months ended March 31, 2019: Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Yrs) Outstanding at December 31, 2018 923,823 $ 3.23 Granted at market price — — Cancelled or expired — — Exercised (17,438 ) 2.11 Outstanding at March 31, 2019 906,385 $ 3.25 4.58 Options exercisable at March 31, 2019 818,885 $ 3.20 4.31 At March 31, 2019, 906,385 stock options outstanding and 818,885 stock options exercisable had an exercise price lower than the market price of the Company’s common stock on that date. The aggregate intrinsic value of these stock options were $3.3 million and $3.0 million, respectively. Restricted Stock Activity The following is a summary of Restricted Stock activity during the three months ended March 31, 2019: Restricted Shares Weighted Average Fair Value Non-vested restricted stock at December 31, 2018 1,355,000 $ 4.58 Granted at market price 1,141,724 7.16 Vested (381,121 ) 4.39 Cancelled (25,000 ) 7.15 Non-vested restricted stock at March 31, 2019 2,090,603 $ 5.95 Restricted Stock Unit Activity The following is a summary of all RSU activity during the three months ended March 31, 2019: Restricted Stock Units Weighted Average Fair Value Non-vested restricted stock units at December 31, 2018 72,168 $ 4.59 Granted at market price 30,000 7.15 Vested (40,334 ) 4.60 Cancelled — — Non-vested restricted stock units at March 31, 2019 61,834 $ 5.82 Performance RSU Activity The following is a summary of all Performance RSU activity during the three months ended March 31, 2019: Performance RSUs Weighted Average Fair Value Non-vested performance RSUs at December 31, 2018 12,499 $ 4.20 Granted at market price 15,000 7.15 Vested (5,777 ) 4.08 Forfeited — — Non-vested performance RSUs at March 31, 2019 21,722 $ 6.27 Performance Stock Activity The following is a summary of all Performance Stock activity during the three months ended March 31, 2019: Performance Stock Weighted Average Fair Value Non-vested performance stock at December 31, 2018 255,626 $ 4.22 Granted at market price 417,500 7.15 Vested (121,558 ) 4.15 Forfeited (25,000 ) 7.15 Non-vested performance stock at March 31, 2019 526,568 $ 6.42 The weighted average grant-date fair value of awards of Restricted Stock, RSUs, Performance RSUs and Performance Stock is based on the quoted market price of the Company’s common stock on the date of grant. Stock-Based Compensation Expense For the three month period ended March 31, 2019, the total stock-based employee compensation expense resulting from stock options, Restricted Stock, RSUs, Performance RSUs and Performance Stock was recorded to the following line items of the Company’s condensed consolidated statements of income: (In thousands) Three Months Ended March 31, 2019 Cost of revenues $ 104 Research and development 175 Selling, general and administrative 950 Stock-based compensation expense $ 1,229 A deferred tax asset totaling $236 thousand and $124 thousand, resulting from stock-based compensation expense associated with awards relating to the Company’s U.S. operations, was recorded for the three month periods ended March 31, 2019 and 2018, respectively. As of March 31, 2019, there was $14.9 million of total unrecognized stock-based compensation expense related to non-vested stock-based compensation awards granted under the incentive plans. This expense is expected to be recognized over a weighted average period of 1.84 years. For additional information regarding the Company’s Equity Awards and Stock-based Employee Compensation, see Note 3, Stock Options and Stock-Based Employee Compensation

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	3 Months Ended
	Mar. 31, 2019
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	4. Supplemental Cash Flow Information Supplemental cash flow information relating to taxes and non-cash activities: Three Months Ended March 31, (In thousands) 2019 2018 Cash income tax payments $ 193 $ 38 Non-cash investing and financing activities: Accrued and deemed dividends on Series A preferred stock 1,982 — Accrued and deemed dividends on Series B preferred stock 451 —

Receivables, Net

Receivables, Net	3 Months Ended
	Mar. 31, 2019
Receivables [Abstract]
Receivables, Net	5. Receivables, net (In thousands) March 31, 2019 December 31, 2018 Gross accounts receivables $ 20,763 $ 14,135 Allowance for returns and doubtful accounts (129 ) (277 ) Unpaid portion of deferred revenue (10,855 ) (10,670 ) Note receivable 458 458 Allowance for note receivable (458 ) (458 ) Receivables, net $ 9,779 $ 3,188 The allowance for doubtful accounts includes all specific accounts receivable which we believe are likely not collectible based on known information. The reduction for the unpaid portion of 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 March 31, 2019.

Leases

Leases	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Leases	6. Leases Effective January 1, 2019, the Company adopted ASC 842, which requires recognition of a right-of-use asset and lease liability for all leases at the commencement date based on the present value of lease payments over the lease term. Additional qualitative and quantitative disclosures regarding the Company's leasing arrangements are also required. The Company adopted ASC 842 prospectively and elected the package of transition practical expedients that does not require reassessment of (1) whether any existing or expired contracts are or contain leases, (2) lease classification and (3) initial direct costs. In addition, the Company has elected other available practical expedients to not separate lease and nonlease components, which consist principally of common area maintenance charges, for all classes of underlying assets and to exclude leases with an initial term of 12 months or less. The Company determines if a contract is or contains a lease at inception. The Company has operating leases for office spaces and data centers. The Company has entered into lease contracts ranging from 1 to 12 years with the majority of leases having terms one to seven years, many of which include options to extend in various increments. Variable lease costs consist primarily of variable common area maintenance, taxes, insurance, parking and utilities. The Company’s leases do not have any residual value guarantees or restrictive covenants. As the implicit rate is not readily determinable for most of the Company’s lease agreements, the Company uses an estimated incremental borrowing rate to determine the initial present value of lease payments. These discount rates for leases are calculated using the Company's interest rate of the term loan. The components of lease costs are as follows: Three Months ended March 31, (In thousands) 2019 Operating lease costs $ 544 Short-term lease costs 288 Variable lease costs 187 Total lease costs $ 1,019 Supplemental cash flow information related to leases are as follows: Three Months ended March 31, (In thousands) 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flow from operating leases $ 555 Right-of-use assets obtained in exchange for lease obligations: Operating leases 4,550 Supplemental balance sheet information related to lease are as follows: March 31, (In thousands) Balance Sheet Classification 2019 Operating Leases Operating lease right-of-use asset Operating lease assets $ 8,932 Current operating lease liabilities Other current liabilities $ 1,203 Noncurrent operating lease liabilities Noncurrent operating lease liabilities 8,880 Total operating lease liabilities $ 10,083 Weighted average remaining lease term and weighted average discount rate are as follows: Weighted Average Remaining Lease Term (Years) Operating leases 4.97 Weighted Average Discount Rate Operating leases 5.79 % Maturities of lease liabilities are as follows: Payments Due by Period - Year ending December 31, 2018 (In thousands) Total Year 1 (1) Years 2 & 3 Years 4 & 5 Beyond 5 Years Operating leases $ 11,810 $ 2,103 $ 4,268 $ 4,159 $ 1,280 Less imputed interest $ (1,727 ) Total $ 10,083 (1) During the quarter ended March 31, 2019, we entered into an operating lease for office space, which has not yet commenced and is expected to be added as a lease liability at a value of approximately $545 thousand. This operating lease will commence in the second quarter of 2019 with lease term of 5 years.

Long-term Debt

Long-term Debt	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Long-term Debt	7. Long-term Debt On February 20, 2019, the Company entered into a credit agreement (the “Credit Agreement”) with a syndicate of lenders and SunTrust Bank as administrative agent, which (1) provided for borrowing in the form of a senior secured term loan facility in an aggregate principal amount of $175 million (the “Term Loan”), (2) provides for a senior secured delayed draw term loan facility in an aggregate principal amount of $10 million (the “Delayed Draw Term Loan Facility”), and (3) provides for a senior secured revolving credit facility in an aggregate principal amount of $25 million, up to $5 million of which is available for letters of credit (the “Revolving Facility” and, together with the Term Loan and the Delayed Draw Term Loan Facility, the “Credit Facilities”). On February 20, 2019, the Term Loan was borrowed in full to pay a portion of the purchase price in connection with the AppRiver acquisition (described below in Note 16 “Acquisitions”) (including certain fees, costs and expenses related thereto). The Credit Facilities are guaranteed by substantially all of the wholly-owned domestic subsidiaries of Zix. Borrowings under the Credit Agreement bear interest, at the Company’s option, at either (1) the adjusted LIBO rate (as defined in the Credit Agreement) plus a margin ranging from 2.50% to 3.50% or (2) the alternate base rate (as defined in the Credit Agreement) plus a margin ranging from 1.50% to 2.50%. The applicable margin varies depending on the Company’s total net leverage ratio. The Credit Facilities are scheduled to mature on February 20, 2024, unless extended in accordance with the terms of the Credit Agreement. The Credit Agreement includes procedures for additional financial institutions to become lenders, or for any existing lender to increase its commitments thereunder, subject to the limits and conditions set forth in the Credit Agreement. Optional prepayments of borrowings under the Credit Facilities are permitted at any time and do not require any prepayment premium (other than reimbursement of the lenders’ breakage and redeployment costs in the case of a prepayment of LIBO rate borrowings). The Credit Agreement contains various financial, operational, and legal covenants. The financial covenant is tested on a quarterly basis, based on the rolling four-quarter period that ends on the last day of each fiscal quarter. The financial covenant requires the Company to maintain a maximum total net leverage ratio of: • 5.50:1.00 for the fiscal quarters ending March 31, 2019 and June 30, 2019; • 5.25:1.00 for the fiscal quarter ending September 30, 2019; • 5.00:1.00 for the fiscal quarters ending December 31, 2019 through June 30, 2020; • 4.75:1.00 for the fiscal quarters ending September 30, 2020 through March 31, 2021; • 4.50:1.00 for the fiscal quarters ending June 30, 2021 through December 31, 2021; and • 4.25:1.00 for the fiscal quarter ending March 31, 2022 and each fiscal quarter thereafter. The non-financial covenants restrict the Company’s ability and the ability of the Company’s restricted subsidiaries to, among other things, incur indebtedness, incur liens, merge with or acquire other entities, make investments, dispose of assets, enter into sale and leaseback transactions, make dividends, distributions or stock repurchases, prepay junior indebtedness, enter into transactions with affiliates, enter into restrictive agreements, and amend organizational documents or the terms of junior indebtedness. The Credit Agreement contains events of default that Zix believes are customary for a secured credit facility. If an event of default relating to bankruptcy or other insolvency events occurs, all obligations under the Credit Agreement will immediately become due and payable. If any other event of default exists under the Credit Agreement, the lenders may accelerate the maturity of the Credit Facilities and exercise other rights and remedies, including foreclosure or other actions against the collateral. If any default exists under the Credit Agreement, or if the Company is unable to make any of the representations and warranties in the Credit Agreement at the applicable time, Zix will be unable to borrow additional funds or have letters of credit issued under the Credit Agreement. Term Loan As of March 31, 2019, the Company had $175 million in principal outstanding under the Term Loan. The Term Loan was fully drawn on February 20, 2019 in the amount of $175 million, and requires quarterly payments of principal of $437,500 beginning on June 30, 2019. In addition to other customary mandatory prepayment requirements, the Term Loan requires annual prepayments based on a percentage of Zix’s excess cash flow, which percentage will reduce if Zix’s total net leverage ratio decreases. At March 31, 2019, the Company had an outstanding debt balance of $168.7 million based on the 6.18% interest rate in effect during the period from February 20, 2019 through March 31, 2019. Included in the balance at March 31, 2019 is $6.3 million of unamortized debt issuance costs. Future principal payments under the Term Loan as of March 31, 2019 are as follows: (In thousands) Year Ending December 31, Amount 2019 $ 1,313 2020 1,750 2021 1,750 2022 1,750 2023 1,750 2024 166,687 175,000 Delayed Draw Term Loan At March 31, 2019, the Company’s Delayed Draw Term Loan Facility was undrawn and is available until August 20, 2019 in an aggregate principal amount of $10 million to use in connection with future acquisitions permitted under the Credit Agreement. Commencing March 23, 2019, Zix began paying a ticking fee on the unused portion of the Delayed Draw Term Loan Facility. In addition, the Delayed Draw Term Loan Facility (if funded) will require 1.00% per annum amortization of the original principal amount borrowed, payable in equal quarterly installments. In addition to other customary mandatory prepayment requirements, the Delayed Draw Term Loan Facility (if funded) will require annual prepayments based on a percentage of Zix’s excess cash flow, which percentage will reduce if Zix’s total net leverage ratio decreases. On May 7, 2019, Zix acquired assets of Cirius Messaging Inc., and Delivery Slip, Inc., its wholly-owned subsidiary, using the Delayed Draw Term Loan to fund this transaction. See below Note 17 “Subsequent Events” for additional information. Revolving Facility The Company also has a Revolving Facility with the lenders, pursuant to which the lenders agreed to make a Revolving Facility available to the Company in an aggregate amount of up to $25 million. Proceeds from the Revolving Facility may be used for working capital and general business purposes, including the financing of permitted acquisitions, investments and restricted payments, subject, in both cases, to the conditions contained in the Credit Agreement. Zix is charged a commitment fee ranging from 0.25% to 0.50% per year on the daily amount of the unused portions of the commitments under the Revolving Facility. As of March 31, 2019, the Revolving Facility was undrawn and available to fund working capital and for other general corporate purposes, including the financing of permitted acquisitions, investments and restricted payments, subject, in both cases, to the conditions contained in the Credit Agreement.

Preferred Stock

Preferred Stock	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Preferred Stock	8. Preferred Stock On February 20, 2019, (the “Original Issuance Date” or “Closing Date”), Zix consummated a private placement pursuant to an investment agreement with an investment fund managed by True Wind Capital and issued an aggregate of $100 million of shares of convertible Preferred Stock (as defined below) at a price of $1,000 per share (the “Stated Value”). 64,914 shares of Series A Convertible Preferred Stock (the “Series A Preferred Stock”) were issued for proceeds of $62.7 million, net of issuance costs of $2.3 million, and 35,086 shares of Series B Convertible Preferred Stock (the “Series B Preferred Stock” and, together with the Series A Preferred Stock, the “Preferred Stock”) were issued for proceeds of $33.9 million, net of issuance costs of $1.2 million. The Preferred Stock is classified outside of stockholders’ equity in temporary equity because the shares contain certain redemption features which require redemption upon a change in control. The Series A Preferred Stock can be immediately converted to common stock up to a cap imposed by Nasdaq Listing Rules prior to Stockholder Approval (as defined below) with the remainder of the conversion value settled in cash. The conversion option of the Series A Preferred Stock was determined to have a beneficial conversion feature which was valued at $1.4 million and was recorded to additional paid-in capital and as a discount to the Series A Preferred Stock. This resulting discount was immediately amortized as the Series A Preferred Stock has no set redemption date but is currently convertible. The Series B Preferred Stock is not convertible without shareholder approval, so no beneficial conversion feature was recognized. Dividends The Stated Value of the Series A Preferred Stock accretes at a fixed rate of 8% per annum, compounded quarterly (“Series A Preferred Dividend”). Apart from the Series A Preferred Dividend, the holders of Series A Preferred Stock are also entitled to receive any dividends paid on common stocks on an "as converted" basis. No dividend will be paid on common stocks until such dividend is paid on the Series A Preferred Stock. The holders of Series B Preferred Stock are entitled to receive dividends accruing daily on a cumulative basis payable quarterly in arrears in cash at a fixed rate of 10% per annum on the Stated Value (the “Preferred Dividend”). The rate will automatically increase by 1% every six months that the Series B Preferred Stock remains outstanding (subject to a cap of 12%). The rate is subject to increase by 0.5% on every three-month anniversary if the Company fails to redeem the Series B Preferred Stock in the event of a change of control of the Company (subject to a 16% cap). All calculations of the Accreted Value (as defined below) of Series A Preferred Stock and the Preferred Dividend of Series B Preferred Stock will be computed on the basis of a 360-day year of twelve 30-day months. Voting Rights Holders of Series A Preferred Stock are entitled to vote, together with the holders of common stock on all matters submitted to a vote of the holders of common stock. Each holder of Series A Preferred Stock shall be entitled to the number of votes equal to the largest number of whole shares of common stock into which all shares of Series A Preferred Stock held by such holder could be converted up to a cap of 10,783,050 shares of common stock imposed by Nasdaq Listing Rules prior to shareholder approval. The vote or consent of the holders of at least a majority of the shares of Series A Preferred Stock outstanding will be necessary for effecting or validating any of the following actions: (i) any amendment, alteration or repeal of the Articles of Incorporation or Series A Certification of Designations that would adversely effect the rights, preferences, privileges or power of the Series A Preferred Stock; (ii) any amendment or alteration to the Articles of Incorporation or any other action to authorize or create, or increase the number of authorized or issued shares of capital stock of the Company convertible into shares of, or ranking senior to, or on a parity basis with, the Series A Preferred Stock as to dividend rights or liquidation rights; (iii) the issuance of shares of Series A Preferred Stock after the Original Issuance Date other than in connection with the conversion of Series B Preferred Stock that was issued on the Original Issuance Date; (iv) any action that would cause the Company to cease to be treated as a domestic corporation for U.S. federal income tax purposes; and (v) the incurrence of any indebtedness of the Company that would cause Zix to exceed a specified leverage ratio. Holders of shares of Series B Preferred Stock are not entitled to vote with holders of common stock on an “as converted” basis. The vote or consent of the holders of at least a majority of the shares of Series B Preferred Stock outstanding will be necessary for effecting or validating any of the following actions: (i) any amendment, alteration or repeal of the Articles of Incorporation or Series B Certification of Designations that would adversely affect the rights, preferences, privileges or power of the Series B Preferred Stock; (ii) any amendment or alteration to the Articles of Incorporation or any other action to authorize or create, or increase the number of authorized or issued shares of capital stock of the Company convertible into shares of, or ranking senior to, or on a parity basis with, the Series B Preferred Stock as to dividend rights or liquidation rights; (iii) the issuance of shares of Series B Preferred Stock; (iv) any action that would cause the Company to cease to be treated as a domestic corporation for U.S. federal income tax purposes; and (v) the incurrence of any indebtedness of the Company that would cause Zix to exceed a specified leverage ratio. Liquidation Preference The Series A Preferred Stock has a liquidation preference equal to the greater of (i) the Stated Value per share as it has accreted as of such date (the “Accreted Value”) and (ii) the amount such holder would have received if the Series A Preferred Stock had converted into common stock immediately prior to such liquidation. The Series B Preferred Stock has a liquidation preference equal to the sum of (i) the Stated Value and (ii) without duplication, any accrued but unpaid Preferred Dividends. Conversion At any time, each Series A Preferred Stock holder may, subject to a cap until approval of common stock holders under Nasdaq Listing Rules (the “Stockholder Approval”) is obtained, elect to convert each share of such holders’ then-outstanding Series A Preferred Stock into (i) the number of shares of common stock equal to the product of (a) the Accreted Value with respect to such share on the conversion date multiplied by (b) the conversion rate (initially of 166.11) as of the applicable conversion date divided by (c) 1,000 plus (ii) cash in lieu of fractional shares. Following the receipt of Stockholder Approval, each share of Series B Preferred Stock will automatically be converted into the number of shares of Series A Preferred Stock equal to the liquidation preference of such share of Series B Preferred Stock divided by the accreted value of a share of Series A Preferred Stock on the date of conversion plus cash in lieu of fractional shares. If Stockholder Approval is not obtained, the Series B Preferred Stock will not be convertible into shares of Series A Preferred Stock or common stock. Optional Redemption by Zix At any time after the fourth anniversary of the Closing Date, Zix may redeem the Series A Preferred Stock for an amount per share of Series A Preferred Stock equal to the Accreted Value per share of the Series A Preferred Stock to be redeemed as of the applicable redemption date multiplied by 1.50. At any time after the fourth anniversary of the Closing Date, the Company may redeem any then-outstanding shares of Series B Preferred Stock for an amount per share of Series B Preferred Stock equal to the liquidation preference per share of the Series B Preferred Stock to be redeemed as of the applicable redemption date multiplied by 1.50. Series B Preferred Stock Holder Redemption Right At any time after the seventh anniversary of the Closing Date, upon 90 days’ prior notice, each Series B Preferred Stock holder may elect to require Zix to redeem the Series B Preferred Stock for an amount per share of Series B Preferred Stock equal to the liquidation preference per share of the Series B Preferred Stock to be redeemed as of the applicable redemption date multiplied by 1.50.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	3 Months Ended
	Mar. 31, 2019
Revenue From Contract With Customer [Abstract]
Revenue from Contracts with Customers	9. Revenue from Contracts with Customers Accounting policies Our Company provides message security solutions as subscription services in which we recognize revenue as our services are rendered. Historically, our contracts have typically been one to three year contracts billed annually. We are increasingly moving toward a monthly billing model. This shift has been largely driven by our recent acquisition activity, including AppRiver. We exclude from the measurement of the transaction price all taxes assessed by a governmental authority that are both imposed on and concurrent with a specific revenue-producing transaction and collected by our company from a customer (e.g., sales, use, value added, and some excise taxes). Disaggregation of Revenue In the three months ended March 31, 2019, we recorded revenue for our services in the following core industry verticals: 47% healthcare, 28% financial services, 7% government sector, and 18% as other. We operate as a single operating segment. Revenue generated from our email protection services represented 100% of our revenues in the three months ended March 31, 2019 and 2018, respectively. Further, we sell our solutions as a bundle, applying significant judgement to allocate transaction prices of our services based on the standalone selling price of our component services. Contract balances Our contract assets include our accounts receivables, discussed above in Footnote 5 “Receivables, net”, and the deferred cost associated with commissions earned by our sales team on securing new, add-on, and renewal contract orders. During the three months ended March 31, 2019, we increased our noncurrent deferred contract asset by $1.5 million resulting from commissions earned by our sales team during the quarter. We also amortized $684 thousand of deferred cost as a selling and marketing expense in the same period. Our deferred cost asset is assessed for impairment on a periodic basis. There were no impairment losses recognized on deferred contract cost assets for the three months ended March 31, 2019. Our contract liabilities consist of deferred revenue representing future customer services which have been billed and collected. The $10.1 million increase to our net deferred revenue is attributed to the acquired balance from our AppRiver acquisition in February 2019. S . Performance obligations As of March 31, 2019, the aggregate amount of the transaction prices allocated to remaining service performance obligations, which represents the transaction price of firm orders less inception to date revenue, was $87.1 million. We expect to recognize approximately $49.9 million of revenue related to this backlog during the remainder of 2019, $22.7 million in 2020, and $14.5 million in periods thereafter. Approximately $16.8 million of our $29.3 million revenue recognized in the three months ended March 31, 2019, was included in our performance obligation balance at the beginning of the period.

Earnings (Loss) Per Share and P

Earnings (Loss) Per Share and Potential Dilution	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Earnings (Loss) Per Share and Potential Dilution	10. Earnings (Loss) Per Share and Potential Dilution Basic earnings (loss) per share are computed using the weighted average number of common shares outstanding for the applicable period. The dilutive effect of potential common shares outstanding is included in diluted earnings (loss) per share. The computations for basic and diluted earnings (loss) per share for the three months ended March 31, 2019 and 2018, respectively, are as follows: Three Months ended March 31, 2019 2018 Basic weighted average common shares 52,713,576 52,875,428 Effect of dilutive securities: Employee and director stock options — 263,757 Restricted Stock — 238,188 RSUs — 27,184 Performance RSUs — 19,194 Performance Stock — 57,353 Series A Preferred Shares — — Series B Preferred Shares — — Dilutive weighted average common shares 52,713,576 53,481,104 During the three months ended March 31, 2019, potential common shares of all securities were excluded from the calculation of diluted loss per share because the awards were anti-dilutive. During the three months ended March 31, 2018, weighted average shares related to 193,250 stock options, 451,022 shares of Restricted Stock, 24,334 RSUs, 3,666 Performance RSUs, and 74,145 shares of Performance Stock were excluded from the calculation of diluted earnings per share because these awards were anti-dilutive.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	11. Commitments and contingencies We have not entered into any material, non-cancelable purchase commitments at March 31, 2019. Claims and Proceedings We are from time to time involved in legal claims, litigation, and other legal proceedings. Although we may incur significant expenses in those matters, we expect no material adverse effect on our operations or financial results from current or concluded legal proceedings.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	12. 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. For certain of the Company’s financial instruments, including cash and cash equivalents, trade receivables, and accounts payable, the fair values approximate the carrying values due to the short-term maturities of these instruments. 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.

Goodwill

Goodwill	3 Months Ended
	Mar. 31, 2019
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill	13. Goodwill The following is a summary of the changes in the carrying amount of goodwill for the three month periods ended March 31, 2019 and 2018: Three Months ended March 31, (In thousands) 2019 2018 Opening balance $ 13,783 $ 8,469 Additions 147,220 — Acquisition adjustments — (901 ) Goodwill $ 161,003 $ 7,568 Our 2019 acquisition of AppRiver resulted in the increase to our goodwill in the three months ended March 31, 2019. Our acquisition adjustments to goodwill in the three month period ended March 31, 2018, reflect the appropriate reallocation of excess purchase price from goodwill to acquired assets and liabilities related to our Greenview and Entelligence Messaging Server purchases. S . We evaluate goodwill for impairment annually in the fourth quarter, or when there is a reason to believe that the value has been diminished or impaired. There were no impairments to goodwill during the periods presented above.

Common Stock Repurchase Program

Common Stock Repurchase Program	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Common Stock Repurchase Program	14. Common Stock Repurchase Program On April 24, 2017, the Company’s board of directors approved a share repurchase program that enables the Company to purchase up to $10 million of its shares of common stock. The share repurchase program expired on May 31, 2018. As such, no shares of common stock was repurchased during the three month period ended March 31, 2019. During the three month period ended March 31, 2018, the Company repurchased 706,994 shares of our common stock under this program at an aggregate cost of $3.1 million.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	15. Income Taxes The operating losses incurred by the Company’s U.S. operations in past years and the resulting net operating losses for U.S. Federal tax purposes are subject to a $22.7 million reserve. Any reduction to this $22.7 million valuation allowance is based on an assessment of future utilization following accounting guidance, which relies largely on historical earnings. Using this methodology, and updating the future taxable earnings estimates based on first quarter 2019 actual earnings, the Company believes the deferred tax asset allowance as of December 31, 2018, will remain unchanged at December 31, 2019. For this reason, the Company has recognized its first quarter 2019 federal deferred tax provision in full. If in prospective periods we conclude our future U.S. federal taxable estimate established at the end of the year will exceed the prior year estimate, the Company will offset its federal deferred tax provision by reducing its valuation allowance by an equal amount, thereby eliminating from its deferred tax provision federal taxes from the Company’s financial statements. The Company will continue to reevaluate the need for its valuation allowance each quarter, following the same assessment methodology described above. Adjusting our valuation allowance could have a significant impact on operating results for each period that it becomes more likely than not that an additional portion of our deferred tax assets will or will not be realized.

Acquisitions

Acquisitions	3 Months Ended
	Mar. 31, 2019
Business Combinations [Abstract]
Acquisitions	16. Acquisitions Acquisition of AppRiver Companies On February 20, 2019, Zix acquired 100% of the equity interest of AR Topco, LLC and its subsidiaries, including AppRiver LLC (“AppRiver” and collectively, the “AppRiver Companies”), for a total purchase price of $276.4 million, including cash consideration of $271.8 million, net of cash acquired , and subject to a customary working capital adjustment. This acquisition complements our strategy to accelerate our offerings into the cloud at the point of initial cloud application purchase and expand our customer base. We financed the acquisition with proceeds from (1) cash on hand, (2) the proceeds from the Term Loan, and (3) a private placement with an investment fund managed by True Wind Capital consisting of (i) 64,914 newly issued shares of Series A Convertible Preferred Stock, $1.00 par value per share, and (ii) 35,086 newly issued shares of Series B Convertible Preferred Stock, $1.00 par value per share in exchange for cash consideration in an aggregate amount of $100 million (which was reduced by $3 million in True Wind Capital’s costs that were reimbursed by the Company). AppRiver is a channel-first provider of cloud-based cyber security and productivity services, offering web protection, email encryption, secure archiving, and email continuity solutions. AppRiver also provides Microsoft Office 365 and Secure Hosted Exchange services, which serve as an effective lead generation tool for AppRiver’s solutions. The acquisition of AppRiver can accelerate our offerings into the cloud at the point of initial cloud application purchase. Because AppRiver currently services over 60,000 worldwide customers using a network of 4,500 Managed Service Providers, this acquisition can help us expand our customer base. The Company incurred $7.8 million in acquisition-related costs which included $1.0 million and $6.8 million recorded within the operating expenses during the three months ended December 31, 2018, and March 31, 2019, respectively. Revenue from AppRiver was $10.9 million for the three months ended March 31, 2018, and due to the continued integration of the combined businesses, it was impracticable to determine earnings. We accounted for the acquisition as the purchase of a business and recorded the excess purchase price as goodwill. The goodwill from this transaction is not yet finalized. The majority of the goodwill balance is expected to be deductible for tax purposes. The intangible assets we acquired from AppRiver consist of customer relationships, vendor relationships, trademark/names, and internally developed software, which we are amortizing over 8 years, 3 years, 10 years, and 5-6 years, respectively. The results of operations and the provisional fair values of the acquired assets and liabilities have been included in the accompanying condensed consolidated financial statements since our AppRiver acquisition on February 20, 2019. Certain estimated values are not yet finalized and subject to revision as additional information becomes available and more detailed analyses are completed. The following table summarizes the estimated fair value of acquired assets and liabilities: (In thousands) Provisional Fair Value Assets: Current assets $ 12,201 Property and equipment 3,291 ROU assets 4,550 Customer relationships 91,000 Vendor relationships 1,000 Trademark/Names 4,400 Internally developed software 41,100 Goodwill 147,220 Total assets 304,762 Liabilities: Current liabilities $ 13,532 Deferred revenue 10,321 Operating lease liabilities 4,550 Total liabilities 28,403 Net assets recorded $ 276,359 Erado On April 2, 2018, the Company acquired all the outstanding capital stock of CM2.COM, Inc., d/b/a Erado (“Erado”) for a total purchase price of $14.4 million, including cash consideration of $11.8 million, net of cash acquired. The purchase of Erado strengthens Zix’s comprehensive archiving solutions with unified archiving, supervision, security, and messaging solutions for customers that demand bundled services. Erado’s long standing focus on helping its customers comply with Financial Industry Regulatory Authority (“FINRA”) and SEC regulations will help further strengthen Zix’s offering for customers with compliance requirements. This acquisition also expands Zix’s cloud-based email archiving capabilities into more than 50 content channels, including social medial, instant message, mobile, web, audio, and video. The purchase price includes a holdback of $2.3 million for the satisfaction of certain indemnification claims by the Company, if any, during the two-year period following the closing of the acquisition. An amount equal to $1.1 million of the holdback amount, less any amounts paid or otherwise subject to an outstanding claim for indemnification, will be released to the selling shareholders upon the one year anniversary of the closing of the acquisition, and the balance of the holdback amount, if any, will be distributed to the Selling Shareholders following the two year anniversary of the closing of the acquisition. The Company incurred $334 thousand in acquisition-related costs which were recorded within operating expenses during twelve months ended December 31, 2018. We accounted for the acquisition as the purchase of a business and recorded the excess purchase price as goodwill. The goodwill from this transaction is deductible for tax purpose. The intangible assets we acquired from Erado consist of trademarks, internally developed software, and customer relationships, which we are amortizing over an estimated useful life of 5 years, 10 years, and 15 years, respectively. The results of operations and the estimated fair values of the acquired assets and liabilities have been included in the accompanying consolidated financial statements since our April 2, 2018, acquisition date. Revenue from Erado was $861 thousand for the three months ended March 31, 2019. Due to the continued integration of the combined businesses, it was impracticable to determine the earnings. The following table summarizes the provisional fair value of acquired assets and liabilities: (In thousands) Estimated Fair Value Assets: Current assets $ 848 Property and equipment 169 Trademark /names 260 Technology 3,030 Customer relationships 4,760 Goodwill 6,215 Total assets 15,282 Liabilities: Deferred revenue $ 809 Other current liabilities 93 Total liabilities 902 Net assets recorded $ 14,380 Pro Forma Financial Information (Unaudited) The following unaudited pro forma financial information presents the combined results of operations for the three month periods ending March 31, 2019 and 2018, respectively, as though the AppRiver and Erado acquisitions that occurred during the reporting period had occurred as of the beginning of the period presented, with adjustments, such as amortization expense of intangible assets and acquisition-related transaction costs, to give effect to pro forma events that are directly attributable to the acquisitions. These unaudited pro forma results are presented for information purposes only and are not necessarily indicative of what the actual results of operations of the combined company would have been if the respective acquisitions had occurred at the beginning of the period presented, nor are they indicative of future results of operations: Three Months Ended March 31, (In thousands, except per share data) 2019 2018 Revenues $ 45,573 $ 38,269 Net income 3,251 671 Basic income (loss) per share attributed to common shareholders $ 0.02 $ (0.03 ) Diluted income (loss) per share attributed to common shareholders $ 0.02 $ (0.03 )

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2019
Subsequent Events [Abstract]
Subsequent Events	17. Subsequent Events On May 7, 2019, we acquired assets of Cirius Messaging Inc., and Delivery Slip, Inc, its wholly owned subsidiary. Zix paid $14 million in cash, subject to certain adjustments. Our acquisition of these assets strengthens our current portfolio with additional email encryption, e-signatures and secure file sharing solutions. The Company is currently in the process of determining the fair value of the assets acquired in this purchase.

Recent Accounting Standards a_2

Recent Accounting Standards and Pronouncements (Policies)	3 Months Ended
	Mar. 31, 2019
Accounting Changes And Error Corrections [Abstract]
Leases	Leases In February 2016, the FASB issued Accounting Standards Update No. 2016-02, Leases (Topic 842). Topic 842 requires companies to generally recognize on the balance sheet operating and financing lease liabilities and corresponding right-of-use assets. We elected the available practical expedients and adopted ASC 842 effective January 1, 2019, prospectively. The adoption of this standard resulted in the recognition of right-to-use assets and lease liabilities of $4.8 million and $6.0 million, with no material impact on the results of operations and cash flows. See below Note 6 “Leases" for additional information regarding our leases.
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. For certain of the Company’s financial instruments, including cash and cash equivalents, trade receivables, and accounts payable, the fair values approximate the carrying values due to the short-term maturities of these instruments. 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.

Stock- Based Awards and Stock_2

Stock- Based Awards and Stock-Based Employee Compensation Expense (Tables)	3 Months Ended
	Mar. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of All Stock Option Transactions	The following is a summary of all stock option transactions during the three months ended March 31, 2019: Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Yrs) Outstanding at December 31, 2018 923,823 $ 3.23 Granted at market price — — Cancelled or expired — — Exercised (17,438 ) 2.11 Outstanding at March 31, 2019 906,385 $ 3.25 4.58 Options exercisable at March 31, 2019 818,885 $ 3.20 4.31
Summary of Restricted Stock Activity	The following is a summary of Restricted Stock activity during the three months ended March 31, 2019: Restricted Shares Weighted Average Fair Value Non-vested restricted stock at December 31, 2018 1,355,000 $ 4.58 Granted at market price 1,141,724 7.16 Vested (381,121 ) 4.39 Cancelled (25,000 ) 7.15 Non-vested restricted stock at March 31, 2019 2,090,603 $ 5.95
Summary of All Restricted Stock Unit Activity	The following is a summary of all RSU activity during the three months ended March 31, 2019: Restricted Stock Units Weighted Average Fair Value Non-vested restricted stock units at December 31, 2018 72,168 $ 4.59 Granted at market price 30,000 7.15 Vested (40,334 ) 4.60 Cancelled — — Non-vested restricted stock units at March 31, 2019 61,834 $ 5.82
Summary of All Performance RSU Activity	The following is a summary of all Performance RSU activity during the three months ended March 31, 2019: Performance RSUs Weighted Average Fair Value Non-vested performance RSUs at December 31, 2018 12,499 $ 4.20 Granted at market price 15,000 7.15 Vested (5,777 ) 4.08 Forfeited — — Non-vested performance RSUs at March 31, 2019 21,722 $ 6.27
Summary of All Performance Stock Activity	The following is a summary of all Performance Stock activity during the three months ended March 31, 2019: Performance Stock Weighted Average Fair Value Non-vested performance stock at December 31, 2018 255,626 $ 4.22 Granted at market price 417,500 7.15 Vested (121,558 ) 4.15 Forfeited (25,000 ) 7.15 Non-vested performance stock at March 31, 2019 526,568 $ 6.42
Summary of Total Stock-based Employee Compensation Expense Resulting from Stock Options, Restricted Stock, RSUs, Performance RSUs, and Performance Stock	For the three month period ended March 31, 2019, the total stock-based employee compensation expense resulting from stock options, Restricted Stock, RSUs, Performance RSUs and Performance Stock was recorded to the following line items of the Company’s condensed consolidated statements of income: (In thousands) Three Months Ended March 31, 2019 Cost of revenues $ 104 Research and development 175 Selling, general and administrative 950 Stock-based compensation expense $ 1,229

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information (Tables)	3 Months Ended
	Mar. 31, 2019
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information Relating to Taxes and Non-Cash Activities	Supplemental cash flow information relating to taxes and non-cash activities: Three Months Ended March 31, (In thousands) 2019 2018 Cash income tax payments $ 193 $ 38 Non-cash investing and financing activities: Accrued and deemed dividends on Series A preferred stock 1,982 — Accrued and deemed dividends on Series B preferred stock 451 —

Receivables, Net (Tables)

Receivables, Net (Tables)	3 Months Ended
	Mar. 31, 2019
Receivables [Abstract]
Summary of Net Receivables	(In thousands) March 31, 2019 December 31, 2018 Gross accounts receivables $ 20,763 $ 14,135 Allowance for returns and doubtful accounts (129 ) (277 ) Unpaid portion of deferred revenue (10,855 ) (10,670 ) Note receivable 458 458 Allowance for note receivable (458 ) (458 ) Receivables, net $ 9,779 $ 3,188

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Schedule of Components of Lease Costs	The components of lease costs are as follows: Three Months ended March 31, (In thousands) 2019 Operating lease costs $ 544 Short-term lease costs 288 Variable lease costs 187 Total lease costs $ 1,019
Schedule of Supplemental Cash Flow Information Related to Leases	Supplemental cash flow information related to leases are as follows: Three Months ended March 31, (In thousands) 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flow from operating leases $ 555 Right-of-use assets obtained in exchange for lease obligations: Operating leases 4,550
Schedule of Supplemental Balance Sheet Information Related to Lease	Supplemental balance sheet information related to lease are as follows: March 31, (In thousands) Balance Sheet Classification 2019 Operating Leases Operating lease right-of-use asset Operating lease assets $ 8,932 Current operating lease liabilities Other current liabilities $ 1,203 Noncurrent operating lease liabilities Noncurrent operating lease liabilities 8,880 Total operating lease liabilities $ 10,083
Schedule of Weighted Average Remaining Lease Term and Weighted Average Discount Rate	Weighted average remaining lease term and weighted average discount rate are as follows: Weighted Average Remaining Lease Term (Years) Operating leases 4.97 Weighted Average Discount Rate Operating leases 5.79 %
Schedule of Maturities of Lease Liabilities	Maturities of lease liabilities are as follows: Payments Due by Period - Year ending December 31, 2018 (In thousands) Total Year 1 (1) Years 2 & 3 Years 4 & 5 Beyond 5 Years Operating leases $ 11,810 $ 2,103 $ 4,268 $ 4,159 $ 1,280 Less imputed interest $ (1,727 ) Total $ 10,083 (1)

Long-term Debt (Tables)

Long-term Debt (Tables)	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Schedule of Future Principal Payments Under Term Loan	Future principal payments under the Term Loan as of March 31, 2019 are as follows: (In thousands) Year Ending December 31, Amount 2019 $ 1,313 2020 1,750 2021 1,750 2022 1,750 2023 1,750 2024 166,687 175,000

Earnings (Loss) Per Share and_2

Earnings (Loss) Per Share and Potential Dilution (Tables)	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Computations of Basic and Diluted Earnings (Loss) Per Share	The computations for basic and diluted earnings (loss) per share for the three months ended March 31, 2019 and 2018, respectively, are as follows: Three Months ended March 31, 2019 2018 Basic weighted average common shares 52,713,576 52,875,428 Effect of dilutive securities: Employee and director stock options — 263,757 Restricted Stock — 238,188 RSUs — 27,184 Performance RSUs — 19,194 Performance Stock — 57,353 Series A Preferred Shares — — Series B Preferred Shares — — Dilutive weighted average common shares 52,713,576 53,481,104

Goodwill (Tables)

Goodwill (Tables)	3 Months Ended
	Mar. 31, 2019
Goodwill And Intangible Assets Disclosure [Abstract]
Summary of Changes in Carrying Amount of Goodwill	The following is a summary of the changes in the carrying amount of goodwill for the three month periods ended March 31, 2019 and 2018: Three Months ended March 31, (In thousands) 2019 2018 Opening balance $ 13,783 $ 8,469 Additions 147,220 — Acquisition adjustments — (901 ) Goodwill $ 161,003 $ 7,568

Acquisitions (Tables)

Acquisitions (Tables)	3 Months Ended
	Mar. 31, 2019
Unaudited Pro Forma Financial Information	The following unaudited pro forma financial information presents the combined results of operations for the three month periods ending March 31, 2019 and 2018, respectively, as though the AppRiver and Erado acquisitions that occurred during the reporting period had occurred as of the beginning of the period presented, with adjustments, such as amortization expense of intangible assets and acquisition-related transaction costs, to give effect to pro forma events that are directly attributable to the acquisitions. These unaudited pro forma results are presented for information purposes only and are not necessarily indicative of what the actual results of operations of the combined company would have been if the respective acquisitions had occurred at the beginning of the period presented, nor are they indicative of future results of operations: Three Months Ended March 31, (In thousands, except per share data) 2019 2018 Revenues $ 45,573 $ 38,269 Net income 3,251 671 Basic income (loss) per share attributed to common shareholders $ 0.02 $ (0.03 ) Diluted income (loss) per share attributed to common shareholders $ 0.02 $ (0.03 )
AppRiver Companies [Member]
Summary of Estimated Fair Value of Acquired Assets and Liabilities	The following table summarizes the estimated fair value of acquired assets and liabilities: (In thousands) Provisional Fair Value Assets: Current assets $ 12,201 Property and equipment 3,291 ROU assets 4,550 Customer relationships 91,000 Vendor relationships 1,000 Trademark/Names 4,400 Internally developed software 41,100 Goodwill 147,220 Total assets 304,762 Liabilities: Current liabilities $ 13,532 Deferred revenue 10,321 Operating lease liabilities 4,550 Total liabilities 28,403 Net assets recorded $ 276,359
Erado [Member]
Summary of Estimated Fair Value of Acquired Assets and Liabilities	The following table summarizes the provisional fair value of acquired assets and liabilities: (In thousands) Estimated Fair Value Assets: Current assets $ 848 Property and equipment 169 Trademark /names 260 Technology 3,030 Customer relationships 4,760 Goodwill 6,215 Total assets 15,282 Liabilities: Deferred revenue $ 809 Other current liabilities 93 Total liabilities 902 Net assets recorded $ 14,380

Recent Accounting Standards a_3

Recent Accounting Standards and Pronouncements - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Feb. 29, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-to-use-assets	$ 8,932
Lease liabilities	$ 10,083
ASU 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-to-use-assets		$ 4,800
Lease liabilities		$ 6,000

Stock- Based Awards and Stock_3

Stock- Based Awards and Stock-Based Employee Compensation Expense - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options outstanding	906,385	923,823
Shares of common stock available for grant	4,320,776
Options, options exercisable	818,885
Deferred tax assets, tax deferred expense compensation and benefits employee compensation	$ 236		$ 124
Total unrecognized stock-based compensation related to non-vested stock-based compensation awards	$ 14,900
The number of years over which expense is expected to be recognized	1 year 10 months 2 days
Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Non-vested stock	2,090,603	1,355,000
Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Non-vested stock	61,834	72,168
Non-vested Performance Stock Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Non-vested stock	526,568	255,626
Non-vested Performance RSUs [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Non-vested stock	21,722	12,499
Employee and Director Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options outstanding	906,385
Options, options exercisable	818,885
Aggregate intrinsic value of options outstanding	$ 3,300
Aggregate intrinsic value of options exercisable	$ 3,000

Stock- Based Awards and Stock_4

Stock- Based Awards and Stock-Based Employee Compensation Expense - Summary of All Stock Option Transactions (Detail)	3 Months Ended
	Mar. 31, 2019$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward
Options, Outstanding, Beginning Balance | shares	923,823
Options, Granted at market price | shares	0
Options, Cancelled or expired | shares	0
Options, Exercised | shares	(17,438)
Options, Outstanding Ending Balance | shares	906,385
Options, Options Exercisable | shares	818,885
Weighted Average Exercise Price, Outstanding, Beginning Balance | $ / shares	$ 3.23
Weighted Average Exercise Price, Granted at market price | $ / shares	0
Weighted Average Exercise Price, Cancelled or expired | $ / shares	0
Weighted Average Exercise Price, Exercised | $ / shares	2.11
Weighted Average Exercise Price, Outstanding, Ending Balance | $ / shares	3.25
Weighted Average Exercise Price, Options Exercisable | $ / shares	$ 3.20
Weighted Average Remaining Contractual Term, Outstanding	4 years 6 months 29 days
Weighted Average Remaining Contractual Term, Options exercisable	4 years 3 months 21 days

Stock- Based Awards and Stock_5

Stock- Based Awards and Stock-Based Employee Compensation Expense - Summary of Restricted Stock Activity (Detail) - Restricted Stock [Member]	3 Months Ended
	Mar. 31, 2019$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, Non-vested, Beginning balance | shares	1,355,000
Shares, Granted at market price | shares	1,141,724
Shares, Vested | shares	(381,121)
Shares, Cancelled | shares	(25,000)
Shares, Non-vested, Ending balance | shares	2,090,603
Weighted Average Fair Value, Non-vested, Beginning balance | $ / shares	$ 4.58
Weighted Average Fair Value, Granted at market price | $ / shares	7.16
Weighted Average Fair Value, Vested | $ / shares	4.39
Weighted Average Fair Value, Cancelled | $ / shares	7.15
Weighted Average Fair Value, Non-vested, Ending balance | $ / shares	$ 5.95

Stock- Based Awards and Stock_6

Stock- Based Awards and Stock-Based Employee Compensation Expense - Summary of All Restricted Stock Unit Activity (Detail) - Restricted Stock Units (RSUs) [Member]	3 Months Ended
	Mar. 31, 2019$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, Non-vested, Beginning balance | shares	72,168
Shares, Granted at market price | shares	30,000
Shares, Vested | shares	(40,334)
Shares, Cancelled | shares	0
Shares, Non-vested, Ending balance | shares	61,834
Weighted Average Fair Value, Non-vested, Beginning balance | $ / shares	$ 4.59
Weighted Average Fair Value, Granted at market price | $ / shares	7.15
Weighted Average Fair Value, Vested | $ / shares	4.60
Weighted Average Fair Value, Cancelled | $ / shares	0
Weighted Average Fair Value, Non-vested, Ending balance | $ / shares	$ 5.82

Stock- Based Awards and Stock_7

Stock- Based Awards and Stock-Based Employee Compensation Expense - Summary of All Performance RSU Activity (Detail) - Non-vested Performance RSUs [Member]	3 Months Ended
	Mar. 31, 2019$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, Non-vested, Beginning balance | shares	12,499
Shares, Granted at market price | shares	15,000
Shares, Vested | shares	(5,777)
Shares, Cancelled | shares	0
Shares, Non-vested, Ending balance | shares	21,722
Weighted Average Fair Value, Non-vested, Beginning balance | $ / shares	$ 4.20
Weighted Average Fair Value, Granted at market price | $ / shares	7.15
Weighted Average Fair Value, Vested | $ / shares	4.08
Weighted Average Fair Value, Cancelled | $ / shares	0
Weighted Average Fair Value, Non-vested, Ending balance | $ / shares	$ 6.27

Stock- Based Awards and Stock_8

Stock- Based Awards and Stock-Based Employee Compensation Expense - Summary of All Performance Stock Activity (Details) - Performance Stock [Member]	3 Months Ended
	Mar. 31, 2019$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, Non-vested, Beginning balance | shares	255,626
Shares, Granted at market price | shares	417,500
Shares, Vested | shares	(121,558)
Shares, Cancelled | shares	(25,000)
Shares, Non-vested, Ending balance | shares	526,568
Weighted Average Fair Value, Non-vested, Beginning balance | $ / shares	$ 4.22
Weighted Average Fair Value, Granted at market price | $ / shares	7.15
Weighted Average Fair Value, Vested | $ / shares	4.15
Weighted Average Fair Value, Cancelled | $ / shares	7.15
Weighted Average Fair Value, Non-vested, Ending balance | $ / shares	$ 6.42

Stock- Based Awards and Stock_9

Stock- Based Awards and Stock-Based Employee Compensation Expense - Summary of Total Stock-based Employee Compensation Expense Resulting from Stock Options, Restricted Stock, RSUs, Performance RSUs, and Performance Stock (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 1,229
Cost of Revenues [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	104
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	175
Selling, General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 950

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information - Supplemental Cash Flow Information Relating to Taxes and Non-Cash Activities (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Supplemental Cash Flow [Line Items]
Cash income tax payments	$ 193	$ 38
Non-cash investing and financing activities:
Accrued and deemed dividends on preferred stock	2,433
Series A Convertible Preferred Stock [Member]
Non-cash investing and financing activities:
Accrued and deemed dividends on preferred stock	1,982
Series B Convertible Preferred Stock [Member]
Non-cash investing and financing activities:
Accrued and deemed dividends on preferred stock	$ 451

Receivables, Net - Summary of N

Receivables, Net - Summary of Net Receivables (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounts Notes And Loans Receivable Net Current [Abstract]
Gross accounts receivables	$ 20,763	$ 14,135
Allowance for returns and doubtful accounts	(129)	(277)
Unpaid portion of deferred revenue	(10,855)	(10,670)
Note receivable	458	458
Allowance for note receivable	(458)	(458)
Receivables, net	$ 9,779	$ 3,188

Receivables, Net - Additional I

Receivables, Net - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Receivables [Abstract]
Note receivable on a product line	$ 540
Date of note receivable, reserved	Mar. 31, 2019

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Lessee Lease Description [Line Items]
Lessee, operating lease, variable lease payment, terms and conditions	Variable lease costs consist primarily of variable common area maintenance, taxes, insurance, parking and utilities.
Lessee, operating lease, existence of option to extend	true
Operating lease liability	$ 545
Lessee, operating lease, lease not yet commenced, term of contract	5 years
Lessee, operating lease, lease not yet commenced, description	During the quarter ended March 31, 2019, we entered into an operating lease for office space, which has not yet commenced and is expected to be added as a lease liability at a value of approximately $545 thousand. This operating lease will commence in the second quarter of 2019 with lease term of 5 years.
Minimum [Member]
Lessee Lease Description [Line Items]
Lessee, operating lease, term of contract	1 year
Lessee, majority operating lease, term of contract	1 year
Maximum [Member]
Lessee Lease Description [Line Items]
Lessee, operating lease, term of contract	12 years
Lessee, majority operating lease, term of contract	7 years

Leases - Schedule of Components

Leases - Schedule of Components of Lease Costs (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Lease Cost [Abstract]
Operating lease costs	$ 544
Short-term lease costs	288
Variable lease costs	187
Total lease costs	$ 1,019

Leases - Schedule of Supplement

Leases - Schedule of Supplemental Cash Flow Information Related to Leases (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flow from operating leases	$ 555
Right-of-use assets obtained in exchange for lease obligations:
Operating leases	$ 4,550

Leases - Schedule of Suppleme_2

Leases - Schedule of Supplemental Balance Sheet Information Related to Lease (Detail) $ in Thousands	Mar. 31, 2019USD ($)
Assets And Liabilities Lessee [Abstract]
Operating lease right-of-use asset	$ 8,932
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	zixi:OperatingLeaseAssetsMember
Current operating lease liabilities	$ 1,203
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherCurrentLiabilitiesMember
Noncurrent operating lease liabilities	$ 8,880
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherNoncurrentLiabilitiesMember
Total operating lease liabilities	$ 10,083

Leases - Schedule of Weighted A

Leases - Schedule of Weighted Average Remaining Lease Term and Weighted Average Discount Rate (Detail)	Mar. 31, 2019
Lease Cost [Abstract]
Operating leases, weighted average remaining lease term (years)	4 years 11 months 19 days
Operating leases, weighted average discount rate	5.79%

Leases - Schedule of Maturities

Leases - Schedule of Maturities of Lease Liabilities (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Operating Lease Liabilities Payments Due [Abstract]
Operating leases	$ 11,810
Less imputed interest	(1,727)
Total	10,083
Operating lease payments due, Year 1	2,103
Operating lease payments due, Years 2 & 3	4,268
Operating lease payments due, Years 4 & 5	4,159
Operating lease payments due, beyond 5 years	$ 1,280

Long-term Debt - Additional Inf

Long-term Debt - Additional Information (Detail)	Mar. 23, 2019	Feb. 20, 2019USD ($)	Mar. 31, 2019USD ($)	Mar. 31, 2019USD ($)
Debt Instrument [Line Items]
Outstanding debt balance			$ 168,700,000	$ 168,700,000
Interest rate			6.18%
Unamortized debt issuance costs			$ 6,300,000	6,300,000
Term Loan [Member]
Debt Instrument [Line Items]
Debt instrument, quarterly payment, principal amount			175,000,000	175,000,000
Lines of credit, drawn amount		$ 175,000,000
Debt instrument quarterly payment, principal amount				437,500
Outstanding debt balance			175,000,000	$ 175,000,000
Credit Agreement [Member]
Debt Instrument [Line Items]
Credit facility maturity date		Feb. 20, 2024
Credit Agreement [Member] | Maximum [Member] | Revolving Facility [Member]
Debt Instrument [Line Items]
Percentage of commitment fee unused portions				0.50%
Credit Agreement [Member] | Maximum [Member] | March 31, 2019 and June 30, 2019 [Member]
Debt Instrument [Line Items]
Maximum total net leverage ratio		5.50
Credit Agreement [Member] | Maximum [Member] | September 30, 2019 [Member]
Debt Instrument [Line Items]
Maximum total net leverage ratio		5.25
Credit Agreement [Member] | Maximum [Member] | December 31, 2019 through June 30, 2020 [Member]
Debt Instrument [Line Items]
Maximum total net leverage ratio		5
Credit Agreement [Member] | Maximum [Member] | September 30, 2020 through March 30, 2021 [Member]
Debt Instrument [Line Items]
Maximum total net leverage ratio		4.75
Credit Agreement [Member] | Maximum [Member] | June 30, 2021 through December 31, 2021 [Member]
Debt Instrument [Line Items]
Maximum total net leverage ratio		4.50
Credit Agreement [Member] | Maximum [Member] | March 31, 2022 and Each Fiscal Quarter Thereafter [Member]
Debt Instrument [Line Items]
Maximum total net leverage ratio		4.25
Credit Agreement [Member] | Maximum [Member] | LIBO Rate [Member]
Debt Instrument [Line Items]
Debt instrument bear interest rate		3.50%
Credit Agreement [Member] | Maximum [Member] | Alternate Base Rate [Member]
Debt Instrument [Line Items]
Debt instrument bear interest rate		2.50%
Credit Agreement [Member] | Minimum [Member] | Revolving Facility [Member]
Debt Instrument [Line Items]
Percentage of commitment fee unused portions				0.25%
Credit Agreement [Member] | Minimum [Member] | LIBO Rate [Member]
Debt Instrument [Line Items]
Debt instrument bear interest rate		2.50%
Credit Agreement [Member] | Minimum [Member] | Alternate Base Rate [Member]
Debt Instrument [Line Items]
Debt instrument bear interest rate		1.50%
Credit Agreement [Member] | Senior Secured Delayed Draw Term Loan Facility [Member]
Debt Instrument [Line Items]
Amortization payments percentage of original aggregate principal amount	1.00%
Credit Agreement [Member] | Syndicate of Lenders and SunTrust Bank [Member] | Senior Secured Delayed Draw Term Loan Facility [Member]
Debt Instrument [Line Items]
Aggregate principal amount			10,000,000	$ 10,000,000
Delayed draw term loan facility availability date				Aug. 20, 2019
Credit Agreement [Member] | Syndicate of Lenders and SunTrust Bank [Member] | Senior Secured Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Aggregate principal amount			$ 25,000,000	$ 25,000,000
AppRiver Companies [Member] | Credit Agreement [Member] | Syndicate of Lenders and SunTrust Bank [Member] | Senior Secured Term Loan Facility [Member]
Debt Instrument [Line Items]
Aggregate principal amount		$ 175,000,000
AppRiver Companies [Member] | Credit Agreement [Member] | Syndicate of Lenders and SunTrust Bank [Member] | Senior Secured Delayed Draw Term Loan Facility [Member]
Debt Instrument [Line Items]
Aggregate principal amount		10,000,000
AppRiver Companies [Member] | Credit Agreement [Member] | Syndicate of Lenders and SunTrust Bank [Member] | Senior Secured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Aggregate principal amount		25,000,000
AppRiver Companies [Member] | Credit Agreement [Member] | Syndicate of Lenders and SunTrust Bank [Member] | Senior Secured Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Letters of credit		$ 5,000,000

Long-term Debt - Schedule of Fu

Long-term Debt - Schedule of Future Principal Payments Under Term Loan (Detail) $ in Thousands	Mar. 31, 2019USD ($)
Debt Instrument [Line Items]
Future principal payments	$ 168,700
Term Loan [Member]
Debt Instrument [Line Items]
2019	1,313
2020	1,750
2021	1,750
2022	1,750
2023	1,750
2024	166,687
Future principal payments	$ 175,000

Preferred Stock - Additional In

Preferred Stock - Additional Information (Detail) - USD ($)	Feb. 20, 2019	Mar. 31, 2019	Dec. 31, 2018
Series A Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Convertible Preferred stock, par value		$ 1	$ 1
Convertible Preferred stock, shares issued	64,914	64,914	0
Issuance of preferred stock in connection with private placement	$ 62,700,000
Preferred stock, net of issuance costs	2,300,000	$ 2,253,000
Beneficial conversion feature of preferred stock	$ 1,400,000	$ (1,407,000)
Series B Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Convertible Preferred stock, par value		$ 1	$ 1
Convertible Preferred stock, shares issued	35,086	35,086	0
Issuance of preferred stock in connection with private placement	$ 33,900,000
Preferred stock, net of issuance costs	1,200,000	$ 1,204,000
Beneficial conversion feature of preferred stock	0
Series A Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock accretion percentage		8.00%
Maximum preferred stock converted for voting rights		10,783,050
Preferred stock conversion description		At any time, each Series A Preferred Stock holder may, subject to a cap until approval of common stock holders under Nasdaq Listing Rules (the “Stockholder Approval”) is obtained, elect to convert each share of such holders’ then-outstanding Series A Preferred Stock into (i) the number of shares of common stock equal to the product of (a) the Accreted Value with respect to such share on the conversion date multiplied by (b) the conversion rate (initially of 166.11) as of the applicable conversion date divided by (c) 1,000 plus (ii) cash in lieu of fractional shares.
Series B Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock accretion percentage		10.00%
Preferred stock dividend rate increase percentage		1.00%
Preferred stock dividend rate increase description		Increase by 1% every six months
Preferred stock cap percentage		12.00%
Preferred stock dividend payment rate increase due to non redemption description		Increase by 0.5% on every three-month
Preferred stock dividend payment rate increase due to non redemption		0.50%
Preferred stock dividend non redemption cap percentage		16.00%
Preference share redemption description		At any time after the seventh anniversary of the Closing Date, upon 90 days’ prior notice, each Series B Preferred Stock holder may elect to require Zix to redeem the Series B Preferred Stock for an amount per share of Series B Preferred Stock equal to the liquidation preference per share of the Series B Preferred Stock to be redeemed as of the applicable redemption date multiplied by 1.50.
True Wind Capital [Member]
Temporary Equity [Line Items]
Aggregate purchase price of preferred stock issued in private placement	$ 100,000,000
Convertible Preferred stock, par value	$ 1,000

Revenue from Contracts with C_2

Revenue from Contracts with Customers - Additional Information (Detail)	1 Months Ended	3 Months Ended
	Feb. 28, 2019USD ($)	Mar. 31, 2019USD ($)Segment	Mar. 31, 2018USD ($)
Disaggregation Of Revenue [Line Items]
Number of operating segment | Segment		1
Percentage of revenue generated from email protection services		100.00%	100.00%
Increased noncurrent deferred contract asset		$ 1,500,000
Impairment losses recognized on deferred contract cost assets		0
Amortization of deferred cost		684,000
Revenue remaining service performance obligations		87,100,000
Revenue recognized performance obligation		16,800,000
Revenue recognized		$ 29,300,000	$ 16,654,000
AppRiver Companies [Member]
Disaggregation Of Revenue [Line Items]
Increase to net deferred revenue	$ 10,100,000
Healthcare [Member]
Disaggregation Of Revenue [Line Items]
Revenue in precentage		47.00%
Financial Services [Member]
Disaggregation Of Revenue [Line Items]
Revenue in precentage		28.00%
Government Sector [Member]
Disaggregation Of Revenue [Line Items]
Revenue in precentage		7.00%
Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue in precentage		18.00%
Minimum [Member]
Disaggregation Of Revenue [Line Items]
Subscription services contracts period		1 year
Maximum [Member]
Disaggregation Of Revenue [Line Items]
Subscription services contracts period		3 years

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Additional Information (Detail 1) $ in Millions	Mar. 31, 2019USD ($)
Disaggregation Of Revenue [Line Items]
Revenue remaining service performance obligations	$ 87.1
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2019-04-01
Disaggregation Of Revenue [Line Items]
Revenue, remaining performance obligation expected timing of satisfaction period	9 months
Revenue remaining service performance obligations	$ 49.9
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2020-01-01
Disaggregation Of Revenue [Line Items]
Revenue, remaining performance obligation expected timing of satisfaction period	1 year
Revenue remaining service performance obligations	$ 22.7
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-01-01
Disaggregation Of Revenue [Line Items]
Revenue, remaining performance obligation expected timing of satisfaction period
Revenue remaining service performance obligations	$ 14.5

Earnings (Loss) Per Share and_3

Earnings (Loss) Per Share and Potential Dilution - Computations of Basic and Diluted Earnings (Loss) Per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Weighted Average Number of Shares [Line Items]
Basic weighted average common shares	52,713,576	52,875,428
Dilutive weighted average common shares	52,713,576	53,481,104
Employee and Director Stock Options [Member]
Weighted Average Number of Shares [Line Items]
Effect of dilutive securities		263,757
Restricted Stock [Member]
Weighted Average Number of Shares [Line Items]
Effect of dilutive securities		238,188
RSUs [Member]
Weighted Average Number of Shares [Line Items]
Effect of dilutive securities		27,184
Performance RSUs [Member]
Weighted Average Number of Shares [Line Items]
Effect of dilutive securities		19,194
Performance Stock [Member]
Weighted Average Number of Shares [Line Items]
Effect of dilutive securities		57,353

Earnings (Loss) Per Share and_4

Earnings (Loss) Per Share and Potential Dilution - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2018shares
Employee and Director Stock Options [Member]
Weighted Average Number of Shares [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	193,250
Restricted Stock [Member]
Weighted Average Number of Shares [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	451,022
RSUs [Member]
Weighted Average Number of Shares [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	24,334
Performance RSUs [Member]
Weighted Average Number of Shares [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	3,666
Performance Stock [Member]
Weighted Average Number of Shares [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	74,145

Goodwill - Summary of Changes i

Goodwill - Summary of Changes in Carrying Amount of Goodwill (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Goodwill Roll Forward
Opening balance	$ 13,783	$ 8,469
Additions	147,220
Acquisition adjustments		(901)
Goodwill	$ 161,003	$ 7,568

Goodwill - Additional Informati

Goodwill - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill impairment	$ 0	$ 0

Common Stock Repurchase Progr_2

Common Stock Repurchase Program - Additional Information (Detail) - USD ($)	Apr. 24, 2017	Mar. 31, 2019	Mar. 31, 2018
Equity, Class of Treasury Stock [Line Items]
Share repurchase program authorized amount	$ 10,000,000
Share repurchase program expiration date	May 31, 2018
Treasury repurchase program			$ 3,090,000
January 2016 Stock Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Shares repurchased		0	706,994
Treasury repurchase program			$ 3,100,000

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) $ in Millions	Mar. 31, 2019USD ($)
Income Tax Disclosure [Abstract]
Operating loss carryforwards	$ 22.7

Acquisitions - Additional Infor

Acquisitions - Additional Information (Detail) $ / shares in Units, $ in Thousands	Feb. 20, 2019USD ($)CustomerServiceProvider$ / sharesshares	Apr. 02, 2018USD ($)Channel	Mar. 31, 2019USD ($)$ / shares	Dec. 31, 2018USD ($)$ / shares	Mar. 31, 2018USD ($)	Dec. 31, 2018USD ($)$ / shares
Business Acquisition [Line Items]
Cash consideration			$ 271,706
Series A Convertible Preferred Stock [Member]
Business Acquisition [Line Items]
Preferred stock, par value | $ / shares			$ 1	$ 1		$ 1
Series B Convertible Preferred Stock [Member]
Business Acquisition [Line Items]
Preferred stock, par value | $ / shares			$ 1	$ 1		$ 1
True Wind Capital [Member]
Business Acquisition [Line Items]
Preferred stock, par value | $ / shares	$ 1,000
Investment agreement aggregate cash consideration	$ 100,000
AppRiver Companies [Member]
Business Acquisition [Line Items]
Percentage of equity interest acquired	100.00%
Total purchase price	$ 276,400
Cash consideration	$ 271,800
Number of customers | Customer	60,000
Number of managed service providers | ServiceProvider	4,500
Business combination, acquisition related costs			$ 7,800
Business combination, revenue					$ 10,900
AppRiver Companies [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Intangible assets, estimated useful live	8 years
AppRiver Companies [Member] | Vendor Relationships [Member]
Business Acquisition [Line Items]
Intangible assets, estimated useful live	3 years
AppRiver Companies [Member] | Trademark/names [Member]
Business Acquisition [Line Items]
Intangible assets, estimated useful live	10 years
AppRiver Companies [Member] | Internally Developed Software [Member] | Minimum [Member]
Business Acquisition [Line Items]
Intangible assets, estimated useful live	5 years
AppRiver Companies [Member] | Internally Developed Software [Member] | Maximum [Member]
Business Acquisition [Line Items]
Intangible assets, estimated useful live	6 years
AppRiver Companies [Member] | Operating Expenses [Member]
Business Acquisition [Line Items]
Business combination, acquisition related costs			6,800	$ 1,000
AppRiver Companies [Member] | True Wind Capital [Member] | Series A Convertible Preferred Stock [Member] | Private Placement [Member]
Business Acquisition [Line Items]
Preferred stock, shares, new issue | shares	64,914
Preferred stock, par value | $ / shares	$ 1
AppRiver Companies [Member] | True Wind Capital [Member] | Series B Convertible Preferred Stock [Member] | Private Placement [Member]
Business Acquisition [Line Items]
Preferred stock, shares, new issue | shares	35,086
Preferred stock, par value | $ / shares	$ 1
AppRiver Companies [Member] | True Wind Capital [Member] | Series A and B Convertible Preferred Stock [Member] | Private Placement [Member]
Business Acquisition [Line Items]
Investment agreement aggregate cash consideration	$ 100,000
Reduction in costs, that were reimbursed	$ 3,000
Erado [Member]
Business Acquisition [Line Items]
Total purchase price		$ 14,400
Cash consideration		$ 11,800
Business combination, acquisition related costs						$ 334
Business combination, revenue			$ 861
Number of channels | Channel		50
Cash consideration paid through escrow deposit		$ 2,300
Escrow account certain indemnification claims, period		2 years
Holdback amount released to selling shareholders upon one year anniversary of closing acquisition		$ 1,100
Holdback released to selling shareholders, description			An amount equal to $1.1 million of the holdback amount, less any amounts paid or otherwise subject to an outstanding claim for indemnification, will be released to the selling shareholders upon the one year anniversary of the closing of the acquisition, and the balance of the holdback amount, if any, will be distributed to the Selling Shareholders following the two year anniversary of the closing of the acquisition.
Erado [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Intangible assets, estimated useful live		15 years
Erado [Member] | Trademarks [Member]
Business Acquisition [Line Items]
Intangible assets, estimated useful live		5 years
Erado [Member] | Internally Developed Software [Member]
Business Acquisition [Line Items]
Intangible assets, estimated useful live		10 years

Acquisitions - Summary of Estim

Acquisitions - Summary of Estimated Fair Value of Acquired Assets and Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Feb. 20, 2019	Dec. 31, 2018	Apr. 02, 2018	Mar. 31, 2018	Dec. 31, 2017
Assets:
Goodwill	$ 161,003		$ 13,783		$ 7,568	$ 8,469
AppRiver Companies [Member]
Assets:
Current assets		$ 12,201
Property and equipment		3,291
ROU assets		4,550
Goodwill		147,220
Total assets		304,762
Liabilities:
Current liabilities		13,532
Deferred revenue		10,321
Total liabilities		28,403
Operating lease liabilities		4,550
Net assets recorded		276,359
AppRiver Companies [Member] | Trademark/names [Member]
Assets:
Intangible assets		4,400
AppRiver Companies [Member] | Customer Relationships [Member]
Assets:
Intangible assets		91,000
AppRiver Companies [Member] | Vendor Relationships [Member]
Assets:
Intangible assets		1,000
AppRiver Companies [Member] | Internally Developed Software [Member]
Assets:
Intangible assets		$ 41,100
Erado [Member]
Assets:
Current assets				$ 848
Property and equipment				169
Goodwill				6,215
Total assets				15,282
Liabilities:
Deferred revenue				809
Other current liabilities				93
Total liabilities				902
Net assets recorded				14,380
Erado [Member] | Trademark/names [Member]
Assets:
Intangible assets				260
Erado [Member] | Customer Relationships [Member]
Assets:
Intangible assets				4,760
Erado [Member] | Technology [Member]
Assets:
Intangible assets				$ 3,030

Acquisitions - Unaudited Pro Fo

Acquisitions - Unaudited Pro Forma Financial Information (Detail) - Erado [Member] - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Business Acquisition [Line Items]
Revenues	$ 45,573	$ 38,269
Net income	$ 3,251	$ 671
Basic income (loss) per share attributed to common shareholders	$ 0.02	$ (0.03)
Diluted income (loss) per share attributed to common shareholders	$ 0.02	$ (0.03)

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) $ in Millions	May 07, 2019USD ($)
Cirius Messaging Inc. and Delivery Slip Inc. [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Cash consideration	$ 14