Navigator (NVGS) 20-F 5 Mar 18 2017 FY Annual report (foreign) Financial data

Document and Entity Information

Document and Entity Information	12 Months Ended
	Dec. 31, 2017shares
Document And Entity Information [Abstract]
Document Type	20-F
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	NVGS
Entity Registrant Name	Navigator Holdings Ltd.
Entity Central Index Key	1,581,804
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding	55,529,762

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 62,109	$ 57,272
Accounts receivable, net	14,889	7,059
Accrued income	15,791	13,134
Prepaid expenses and other current assets	10,964	8,541
Bunkers and lubricant oils	8,008	6,937
Insurance recoverable	376	855
Total current assets	112,137	93,798
Non-current assets
Vessels under construction		150,492
Property, plant and equipment, net	1,611	194
Total non-current assets	1,741,750	1,631,045
Total assets	1,853,887	1,724,843
Current liabilities
Current portion of secured term loan facilities, net of deferred financing costs	81,559	78,464
Senior unsecured bond		25,000
Accounts payable	8,071	6,388
Accrued expenses and other liabilities	12,478	11,377
Accrued interest	3,500	2,932
Deferred income	4,824	3,522
Total current liabilities	110,432	127,683
Non-current Liabilities
Secured term loan facilities, net of current portion and deferred financing costs	681,658	540,680
Senior unsecured bond, net of deferred financing costs	98,584	100,000
Total non-current liabilities	780,242	640,680
Total Liabilities	890,674	768,363
Commitments and contingencies (see note 12)
Stockholders' equity
Common stock-$.01 par value per share; 400,000,000 shares authorized; 55,529,762 shares issued and outstanding, (2016: 55,436,087)	555	554
Additional paid-in capital	589,436	588,024
Accumulated other comprehensive loss	(277)	(287)
Retained earnings	373,499	368,189
Total stockholders' equity	963,213	956,480
Total liabilities and stockholders' equity	1,853,887	1,724,843
Vessels In Operation [Member]
Non-current assets
Property, plant and equipment, net	$ 1,740,139	$ 1,480,359

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Common stock, par value	$ 0.01	$ 0.01
Common stock, authorized	400,000,000	400,000,000
Common stock, shares issued	55,529,762	55,436,087
Common stock, shares outstanding	55,529,762	55,436,087

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Operating revenue	$ 298,595	$ 294,112	$ 315,223
Revenues, Total	298,595	294,112	315,223
Expenses
Brokerage commissions	5,368	5,812	6,995
Voyage expenses	55,542	42,201	33,687
Vessel operating expenses	100,968	90,854	78,842
Depreciation and amortization	73,588	62,280	53,453
General and administrative costs	13,816	12,528	11,011
Other corporate expenses	2,131	1,976	2,553
Profit from sale of vessel			(550)
Vessel write down following collision			10,500
Insurance recoverable from vessel repairs		504	(9,892)
Total operating expenses	251,413	216,155	186,599
Operating income	47,182	77,957	128,624
Other income/(expense)
Interest expense	(37,691)	(32,321)	(28,085)
Write off of deferred finance costs	(786)	(102)	(1,797)
Write off of call premium and redemption charges of 9.00% unsecured bond	(3,517)
Interest income	519	281	152
Income before income taxes	5,707	45,815	98,894
Income taxes	(397)	(1,177)	(800)
Net income	$ 5,310	$ 44,638	$ 98,094
Earnings per share:
Basic:	$ 0.10	$ 0.81	$ 1.77
Diluted:	$ 0.10	$ 0.80	$ 1.76
Weighted average number of shares outstanding:
Basic:	55,508,974	55,418,626	55,360,004
Diluted:	55,881,454	55,794,481	55,706,104

Consolidated Statements of Inc5

Consolidated Statements of Income (Parenthetical)	Dec. 31, 2017	Feb. 10, 2017	Dec. 31, 2016	Dec. 31, 2015
2012 Senior Unsecured Bonds [Member]
Interest rate on bond	9.00%	9.00%	9.00%	9.00%

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 5,310	$ 44,638	$ 98,094
Other comprehensive (loss) / income:
Foreign currency translation (loss) / gain	10	178	(211)
Total comprehensive income	$ 5,320	$ 44,816	$ 97,883

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Issued March 17, 2015 [Member]	Issued March 23, 2017 [Member]	Common Stock [Member]	Common Stock [Member]Issued March 17, 2015 [Member]	Common Stock [Member]Issued March 29, 2016 [Member]	Common Stock [Member]Issued March 23, 2017 [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]
Beginning Balance at Dec. 31, 2014	$ 810,564			$ 553				$ 584,808	$ (254)	$ 225,457
Restricted shares issued		$ 1			$ 1
Beginning Balance, (in shares) at Dec. 31, 2014				55,346,613
Restricted shares issued, (in shares)					16,854
Net income	98,094									98,094
Foreign currency translation	(211)								(211)
Share-based compensation plan	1,643							1,643
Ending Balance at Dec. 31, 2015	910,091			$ 554				586,451	(465)	323,551
Ending Balance, (in shares) at Dec. 31, 2015				55,363,467
Restricted shares issued, (in shares)						72,620
Net income	44,638									44,638
Foreign currency translation	178								178
Share-based compensation plan	1,573							1,573
Ending Balance at Dec. 31, 2016	$ 956,480			$ 554				588,024	(287)	368,189
Ending Balance, (in shares) at Dec. 31, 2016	55,436,087			55,436,087
Restricted shares issued			$ 1				$ 1
Restricted shares issued, (in shares)							93,675
Net income	$ 5,310									5,310
Foreign currency translation	10								10
Share-based compensation plan	1,412							1,412
Ending Balance at Dec. 31, 2017	$ 963,213			$ 555				$ 589,436	$ (277)	$ 373,499
Ending Balance, (in shares) at Dec. 31, 2017	55,529,762			55,529,762

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net income	$ 5,310	$ 44,638	$ 98,094
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	73,588	62,280	53,453
Payment of drydocking costs	(268)	(9,902)	(11,558)
Amortization of share-based compensation	1,412	1,573	1,643
Amortization of deferred financing costs	3,217	3,091	4,806
Call option premium on redemption of 9.00% unsecured bond	2,500
Prior year expenses recovered from insurance claim	(504)
Insurance claim debtor	(7)	60	(10,289)
Vessel write down following collision			10,500
Profit from sale of vessel			(550)
Unrealized foreign exchange	3	208	(205)
Changes in operating assets and liabilities
Accounts receivable	(7,831)	1,991	(1,855)
Bunkers and lubricant oils	(1,074)	(3,457)	1,331
Prepaid expenses and other current assets	(5,079)	(7,694)	(4,408)
Accounts payable, accrued interest and other liabilities	4,654	(6,040)	8,394
Long-term accounts receivable			198
Net cash provided by operating activities	75,921	86,748	149,554
Cash flows from investing activities
Payment to acquire vessels	(1,940)	(1,733)	(3,348)
Payment for vessels under construction	(180,629)	(239,179)	(236,648)
Purchase of other property, plant and equipment	(1,726)	(75)	(142)
Receipt of shipyard penalty payments	280	1,901	1,933
Placement of short term investment	(25,000)
Release of short term investment	25,000
Insurance recoveries	990	9,374	391
Capitalized costs for the repair of Navigator Aries		(8,441)
Proceeds from sale of vessel net of costs			31,958
Net cash used in investing activities	(183,025)	(238,153)	(205,856)
Cash flows from financing activities
Proceeds from secured term loan facilities	395,170	327,670	157,700
Issuance of 7.75% senior unsecured bonds	100,000
Repayment of 9.00% senior unsecured bonds	(127,500)
Issuance cost of 7.75% senior unsecured bonds	(1,819)
Direct financing cost of secured term loan facilities	(2,058)	(2,680)	(5,879)
Repayment of secured term loan facilities	(251,852)	(204,092)	(70,266)
Net cash provided by financing activities	111,941	120,898	81,555
Net increase/(decrease) in cash and cash equivalents	4,837	(30,507)	25,253
Cash and cash equivalents at beginning of year	57,272	87,779	62,526
Cash and cash equivalents at end of year	62,109	57,272	87,779
Supplemental Information
Total interest paid during the year, net of amounts capitalized	35,890	29,815	24,427
Total tax paid during the year	$ 515	$ 601	$ 632

Consolidated Statements of Cas9

Consolidated Statements of Cash Flows (Parenthetical)	Dec. 31, 2017	Feb. 10, 2017	Dec. 31, 2016	Dec. 31, 2015
2017 Senior Unsecured Bonds [Member]
Interest rate on bond	7.75%	7.75%	7.75%	7.75%
2012 Senior Unsecured Bonds [Member]
Interest rate on bond	9.00%	9.00%	9.00%	9.00%

Description of Business

Description of Business	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Description of Business	1. Description of Business Navigator Holdings Ltd. (the “Company”), the ultimate parent company of the Navigator Group of companies, is registered in the Republic of the Marshall Islands. The Company has a business of owning and operating a fleet of gas carriers. At December 31, 2017, the Company owned and operated 38 gas carriers (the “Vessels”) each having a cargo capacity of between 20,085 cbm and 38,000 cbm, of which 31 were semi-refrigerated, and seven were fully-refrigerated vessels.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies (a) Basis of Presentation The consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). The accompanying consolidated financial statements include the accounts of the Company and its subsidiaries (See Note 7) and a Variable Interest Entity (“VIE”). All intercompany accounts and transactions have been eliminated in consolidation. As of December 31, 2017 the Company has consolidated 100% of PT Navigator Khatulistiwa, a VIE for which the Company is deemed to be the primary beneficiary, i.e. it has a controlling financial interest in this entity. The Company owns 49% of the VIE’s common stock, all of its secured debt and has voting control. All economic interests in the residual net assets reside with the Company. A VIE is an entity that in general does not have equity investors with voting rights or that has equity investors that do not provide sufficient financial resources for the entity to support its activities. A controlling financial interest in a VIE is present when a company has the power to direct the activities of a VIE that most significantly impact the entity’s economic performance and has the right to residual gains or the obligation to absorb losses that could potentially be significant to the VIE. During the year ended December 31, 2017, the Company adopted Accounting Standards Update (“ASU”) 2015-17, During the year ended December 31, 2017, the Company adopted ASU 2016-09, (b) Vessels in Operation The cost of the vessels (excluding the estimated initial drydocking cost) less their estimated residual value is depreciated on a straight-line basis over the vessel’s estimated economic life. Management estimates the useful life of each of the Company’s vessels to be 30 years from the date of its original construction. (c) Vessels Under Construction Vessels under construction are stated at cost, which includes the cost of construction, capitalized interest and other direct costs attributable to the construction. No provision for depreciation is made on construction in progress until such time as the relevant assets are completed and put into use. (d) Impairment of Vessels Our vessels are reviewed for impairment when events or circumstances indicate the carrying amount of the vessel may not be recoverable. When such indicators are present, a vessel is tested for recoverability and we recognize an impairment loss if the sum of the future cash flows (undiscounted and excluding interest charges that will be recognized as an expense when incurred) expected to be generated by the vessel over its estimated remaining useful life are less than its carrying value. If we determine that a vessel’s undiscounted cash flows are less than its carrying value, we record an impairment loss equal to the amount by which its carrying amount exceeds its fair value. The new lower cost basis would result in a lower annual depreciation than before the impairment. Considerations in making such an impairment evaluation include comparison of current carrying values to anticipated future operating cash flows, expectations with respect to future operations and other relevant factors. The estimates and assumptions regarding expected cash flows require considerable judgment and are based upon historical experience, financial forecasts and industry trends and conditions. (e) Drydocking Costs Each vessel is required to be dry-docked dry-dockings dry-docking. dry-docking dry-docking (f) Cash and Cash Equivalents The Company considers highly liquid investments, such as time deposits and certificates of deposit, with an original maturity of three months or less when purchased, to be cash equivalents. The Company has cash in a U.S. financial institution which is insured by the Federal Deposit Insurance Corporation (“FDIC”) for up to $0.3 million. At December 31, 2017 and 2016 and for the years then ended, the Company had balances in this financial institution in excess of the insured amount. The Company also maintains cash balances in foreign financial institutions which are not covered by the FDIC. (g) Short-Term Investments Short-term investments represent funds deposited in money market funds with an original maturity of more than three months when purchased. The Company records its short-term investments at fair value. Fair value is a market-based measurement that is determined based on assumptions that market participants would use in pricing an asset or a liability. The fair value hierarchy also requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The Company’s short-term investments are classified within Level 1 of the fair value hierarchy. (h) Accounts Receivable, net The Company carries its accounts receivable at cost less an allowance for doubtful accounts. At December 31, 2017 and 2016, the Company evaluated its accounts receivable and established an allowance for doubtful accounts, based on a history of past write-offs, collections and current credit conditions. The Company does not generally charge interest on past-due past-due (i) Bunkers and lubricant oils Bunkers and lubricant oils include bunkers (fuel), for those vessels under voyage charter, and lubricants. Under a time charter, the cost of bunkers is borne by and remains the property of the charterer. Bunkers and lubricant oils are accounted for on a first in, first out basis and are valued at cost. (j) Deferred Finance Costs Costs incurred in connection with obtaining secured term loan facilities, revolving credit facilities and bonds are recorded as deferred financing costs and are amortized to interest expense over the estimated duration of the related debt. Such costs include fees paid to the lenders or on the lenders’ behalf and associated legal and other professional fees. Under the Accounting Standards Update (ASU) 2015- 03, Interest—Imputation of Interest the Company has adopted the accounting standard (Subtopic 835-30)—simplifying (k) Deferred Income Deferred income is the balance of cash received in excess of revenue earned under a time charter or voyage charter arrangement as of the balance sheet date. (l) Revenue Recognition The Company employs its vessels on time charters, voyage charters or COA’s. With time charters, the Company receives a fixed charter hire per on-hire (m) Other Comprehensive Income / (Loss) The Company follows the provisions of ASC Topic 220 “Comprehensive Income,” which requires separate presentation of certain transactions, which are recorded directly as components of stockholders’ equity. Comprehensive income is comprised of net income and foreign currency translation gains and losses. (n) Voyage Expenses and Vessel Operating Expenses When the Company employs its vessels on time charter, it is responsible for all the operating expenses of the vessels, such as crew costs, stores, insurance, repairs and maintenance. In the case of voyage charters, the vessel is contracted only for a voyage between two or more ports, and the Company pays for all voyage expenses in addition to the vessel operating expenses. Voyage expenses consist mainly of in port expenses and bunker (fuel) consumption and are recognized as incurred. (o) Repairs and Maintenance All expenditures relating to routine maintenance and repairs are expensed when incurred. (p) Insurance The Company maintains hull and machinery insurance, war risk insurance, protection and indemnity insurance coverage, increased value insurance, demurrage and defense insurance coverage in amounts considered prudent to cover normal risks in the ordinary course of its operations. Premiums paid in advance to insurance companies are recognized as prepaid expenses and recorded as a vessel operating expense over the period covered by the insurance contract. In addition, the Company maintains Directors and Officers insurance. (q) Share-Based Compensation The Company records as an expense in its financial statements the fair value of all equity-settled stock-based compensation awards. The terms and vesting schedules for share-based awards vary by type of grant. Generally, the awards vest subject to time-based (immediate to five years) service conditions. Compensation expense is recognized ratably over the service period. (r) Critical Accounting Estimates The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ materially from these estimates. (s) Foreign Currency Transactions Substantially all of the Company’s cash receipts are in U.S. Dollars. The Company’s disbursements, however, are in the currency invoiced by the supplier. The Company remits funds in the various currencies invoiced. The non U.S. Dollar invoices received, and their subsequent payments, are converted into U.S. Dollars when the transactions occur. The movement in exchange rates between these two dates is transferred to an exchange difference account and is expensed each month. The exchange risk resulting from these transactions is not material. (t) Income Taxes Navigator Holdings Ltd. and its Marshall Islands subsidiaries are currently not required to pay income taxes in the Marshall Islands on ordinary income or capital gains as they qualify as exempt companies. The Company has four subsidiaries incorporated in the United Kingdom where the base tax rate is 19%. One UK subsidiary earns management and other fees from fellow subsidiary companies. The second UK subsidiary holds an investment in our VIE and has a loan to our group subsidiary in Poland. The third subsidiary earns management fees from fellow subsidiary companies. The fourth subsidiary was dormant as at December 31, 2017. The Company has a subsidiary in Poland where the base tax rate is 19%. The Company has a subsidiary incorporated in Singapore where the base tax rate is 17%. The subsidiary earns management and other fees and receives interest from its VIE, PT Navigator Khatulistiwa, The Company considered the income tax disclosure requirements of ASC Topic 740 “Income Taxes,” with regard to disclosing material unrecognized tax benefits; none were identified. The Company’s policy is to recognize accrued interest and penalties for unrecognized tax benefits as a component of tax expense. At December 31, 2017 and 2016, there were no accrued interest and penalties for unrecognized tax benefits. (u) Earnings Per Share Basic earnings per common share (“Basic EPS”) is computed by dividing the net income available to common stockholders by the weighted-average number of shares outstanding. Diluted earnings per common share (“Diluted EPS”) are computed by dividing the net income available to common stockholders by the weighted average number of common shares and dilutive common share equivalents then outstanding. Shares granted pursuant to the 2013 Restricted Stock Plan are the only dilutive shares, and these shares have been considered as outstanding since their respective grant dates for purposes of computing diluted earnings per share. (v) Segment Reporting Although separate vessel financial information is available, Management internally evaluates the performance of the enterprise as a whole and not on the basis of separate business units or different types of charters. As a result, the Company has determined that it operates as one reportable segment. Since the Company’s vessels regularly move between countries in international waters over many trade routes, it is impractical to assign revenues or earnings from the transportation of international LPG and petrochemical products by geographic area. (w) Recent Accounting Pronouncements The following accounting standards issued as of December 31, 2017, may affect the future financial reporting by Navigator Holdings Ltd: In May 2014, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2014-09, The effective date for ASU 2014-09 2015-14 During the last year the Company has taken part in a series of discussions with a collective of global shipping companies, to ensure key industry specifics have been considered, as well as to consider the differing views within the industry in order to give maximum consideration to the implementation of the new standard. The Company has assessed the potential impact that the adoption of this guidance will have on its financial statements and footnote disclosures, as well as understanding the implications for the company’s internal processes, systems and controls. The adoption of this standard will have little or no impact on the timing or amounts of revenue recognized for our vessels that operate on time charters. For vessels undertaking voyage charters or contracts of affreightment, we determined that the period over which revenue is recognized will change as a result of adopting this standard. The current policy recognizes revenue beginning from the later of the previous discharge port or the charter party date across the period to the date discharge is completed. Under the new standard, revenue will be recognized beginning from load port across the period to the date discharge is complete, reducing the period of time over which revenue is recognized. The Company has calculated that the effect of this change would result in an increase in the amount of revenue earned and recognized for the year ended December 31, 2017 by a net of $ 0.5 million. The adoption of the new revenue recognition standard will also have an impact on related voyage expenses as certain costs incurred to fulfill a contract or performance obligation can be deferred and amortized over the period of the voyage. The Company has calculated that the effect of this change would result in a reduction in the amount of voyage expenses recognized in the financial statements for the year ended December 31, 2017 by a net of $0.2 million. The Company has also considered the impact on reporting under ASC 606 and has adapted its internal processes and controls to reflect the changes. The Company is also considering the impact on Time Charter Equivalent or “TCE”, a non-GAAP In February 2016, the FASB issued ASU 2016-02, on-balance 2016-02 2016-02 not-for-profit 2016-02 In June 2016, the FASB issued ASU 2016–13, Financial Instruments – Credit Losses, which changes the recognition model for the impairment of financial instruments, including accounts receivable, loans and held-to-maturity In August 2016, the FASB issued ASU 2016-15, • Debt prepayment or debt extinguishment costs; • Settlement of zero-coupon • Contingent consideration payments made after a business combination; • Proceeds from the settlement of insurance claims; • Proceeds from the settlement of corporate-owned life insurance policies, including bank-owned life insurance policies; • Distributions received from equity method investees; • Beneficial interests in securitization transactions; and • Separately identifiable cash flows and application of the predominance principle. This ASU is effective for public business entities for annual and interim periods in fiscal years beginning after December 15, 2017. For all other entities, the ASU is effective for annual periods in fiscal years beginning after December 15, 2018. The Company will adopt this standard beginning January 1, 2018. The impact of adopting this ASU will be immaterial to the financial statements. In November 2016, the FASB issued ASU 2016-18,

Fair Value of Financial Instrum

Fair Value of Financial Instruments Not Accounted For at Fair Value	12 Months Ended
	Dec. 31, 2017
Investments, All Other Investments [Abstract]
Fair Value of Financial Instruments Not Accounted For at Fair Value	3. Fair Value of Financial Instruments Not Accounted For at Fair Value The principal financial assets of the Company at December 31, 2017 and 2016 consist of cash and cash equivalents, and accounts receivable. The principal financial liabilities of the Company consist of accounts payable, accrued expenses and other liabilities, secured term loan facilities, a revolving credit facility and the 7.75% senior unsecured bond issue. The carrying values of cash and cash equivalents, accounts receivable, accounts payable, accrued expenses and other liabilities are reasonable estimates of their fair value due to the short-term nature or liquidity of these financial instruments. Fair value is a market-based measurement that is determined based on assumptions that market participants would use in pricing an asset or a liability. The fair value accounting standard establishes a three tier fair value hierarchy, which prioritizes the inputs used in the valuation methodologies in measuring fair value: Level 1—Observable inputs that reflect quoted prices (unadjusted) for identical assets or liabilities in active markets. Level 2—Include other inputs that are directly or indirectly observable in the marketplace. Level 3—Unobservable inputs which are supported by little or no market activity. The fair value hierarchy also requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The 7.75% unsecured bond issue is classified as a level two liability and the fair value has been calculated based on the most recent trades of the bond on the Oslo Børs prior to December 31, 2017. The fair value of secured term loan facilities and revolving credit facility is estimated based on the average of the current rates offered to the Company for all debt facilities. The carrying value approximates the fair market value for the floating rate loans and revolving credit facilities due to their variable interest rate, being LIBOR. This has been categorized at level three on the fair value measurement hierarchy. The following table includes the estimated fair value and carrying value of those assets and liabilities. The table excludes accounts receivable, the insurance debtor recoverable and accounts payable. December 31, 2016 December 31, 2017 Fair Value Hierarchy Level Fair Carrying Fair Value Carrying Fair Value (in thousands) Cash and cash equivalents Level 1 57,272 57,272 62,109 62,109 Senior unsecured bond (note 9) Level 2 (125,000 ) (127,423 ) (100,000 ) (96,775 ) Secured term loan facilities and revolving credit facility (note 8) Level 3 (628,872 ) (553,346 ) (772,191 ) (636,220 )

Accounts Receivable, Net

Accounts Receivable, Net	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Accounts Receivable, Net	4. Accounts Receivable, Net It is a condition of time charter parties that payments of hire are received monthly in advance. Voyage charter contracts require payment upon completion of each discharge, with subsequent demurrage claims payable on submission of invoices. At December 31, 2017, management has provided a provision for doubtful accounts of $0.3 million relating to outstanding demurrage claims (2016: $0.2 million).

Vessels

Vessels	12 Months Ended
	Dec. 31, 2017
Vessels Under Construction [Member]
Vessels	6. Vessels Under Construction 2016 2017 Vessels under construction at January 1 $ 170,776 $ 150,492 Payments to shipyard 221,532 174,131 Other payments including initial stores and site costs 12,580 4,783 Capitalized interest 5,067 1,715 Transfer to vessels in operation (259,463 ) (331,121 ) Vessels under construction at December 31 $ 150,492 $ —
Vessels In Operation [Member]
Vessels	5. Vessels in Operation Vessel Drydocking Total Cost December 31, 2015 $ 1,462,136 $ 26,729 $ 1,488,865 Additions 10,176 9,902 20,078 Transfer in from vessels under construction 256,663 2,800 259,463 Disposals — (5,482 ) (5,482 ) Reduction in contract cost of newbuild vessels (1,484 ) — (1,484 ) December 31, 2016 1,727,491 33,949 1,761,440 Additions 1,940 268 2,208 Transfer in from vessels under construction 327,571 3,550 331,121 Disposals — (1,492 ) (1,492 ) Reduction in contract cost of newbuild vessels (280 ) — (280 ) December 31, 2017 2,056,722 36,275 2,092,997 Accumulated Depreciation December 31, 2015 $ 215,024 $ 9,390 $ 224,414 Charge for the period 53,653 8,496 62,149 Disposals for the period — (5,482 ) (5,482 ) December 31, 2016 268,677 12,404 281,081 Charge for the period 64,031 9,238 73,269 Disposals for the period — (1,492 ) (1,492 ) December 31, 2017 332,708 20,150 352,858 Net Book Value December 31, 2015 $ 1,247,112 $ 17,339 $ 1,264,451 December 31, 2016 $ 1,458,814 $ 21,545 $ 1,480,359 December 31, 2017 $ 1,724,014 $ 16,125 $ 1,740,139 During 2017 the Company took delivery of two semi-refrigerated midsize liquefied gas carriers from Jiangnan shipyard for a combined contract price of $156.8 million and two semi-refrigerated handysize and one fully refrigerated liquefied gas carriers from HMD shipyard for a combined contract price of $152.5 million. In 2016 the Company took delivery of two semi-refrigerated handysize liquefied gas carriers and two midsize semi-refrigerated ethylene capable liquefied gas carriers from Jiangnan shipyard for a combined contract price of $243.8 million. The net book value of vessels that serve as collateral for the Company’s secured term loan and revolving credit facilities (Note 8) was $1,591 million at December 31, 2017.

Group Subsidiaries

Group Subsidiaries	12 Months Ended
	Dec. 31, 2017
Schedule of Investments [Abstract]
Group Subsidiaries	7. Group Subsidiaries At December 31, 2017 and 2016, the company had the following significant subsidiaries: Corporation Name Percentage Ownership as of December 31, Country of Incorporation Subsidiary of Limited Liability Company 2016 2017 - Navigator Gas US L.L.C. 100 % 100 % Delaware (USA) Service company - Navigator Gas L.L.C. 100 % 100 % Marshall Islands Holding company ~ Navigator Aries 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Atlas L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Aurora L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Centauri L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Ceres L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Ceto L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Copernico L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Capricorn L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Eclipse L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Europa L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Galaxy L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Gemini L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Genesis L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Glory L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Grace L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Gusto L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Jorf L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Leo L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Libra L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Luga L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Magellan L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Mars L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Neptune L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Nova L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Oberon L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Pegasus L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Phoenix L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Prominence L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Saturn L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Scorpio L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Taurus L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Triton L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Umbrio L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Venus L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Virgo L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Yauza L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ NGT Services (UK) Ltd 100 % 100 % England Service company ~ NGT Services (Poland) Sp. Z O.O 100 % 100 % Poland Service company ~ Navigator Gas Ship Management Ltd. 100 % 100 % England Service company ~ Falcon Funding PTE Ltd 100 % 100 % Singapore Service company ~ Navigator Gas Invest Ltd 100 % 100 % England Investment company - PT Navigator Khatulistiwa 49 % 49 % Indonesia Vessel-owning company ~ Navigator Terminals L.L.C. n/a * 100 % Marshall Islands Investment company ~ Navigator Terminals Invest Ltd n/a * 100 % England Investment company - Navigator Ethylene Terminals L.L.C. n/a * 100 % Delaware (USA) Investment company - Enterprise Navigator Ethylene Terminal L.L.C. n/a * 50 % Texas (USA) Terminal operator * Entities formed during 2017. The VIE, PT Navigator Khatulistiwa, had total assets and liabilities, as of December 31, 2017, of $132.2 million (2016: $137.5 million) and $54.4 million (2016: $73.0 million) respectively.

Secured Term Loan Facilities an

Secured Term Loan Facilities and Revolving Credit Facility	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Secured Term Loan Facilities and Revolving Credit Facility	8. Secured Term Loan Facilities and Revolving Credit Facility The table below represents the annual principal payments to be made under our term loans and revolving credit facilities after December 31, 2017: December 31, December 31, Due within one year $ 81,128 $ 83,352 Due in two years 188,586 70,600 Due in three years 41,823 128,725 Due in four years 99,948 60,600 Due in five years 31,823 302,461 Due in more than five years 185,564 126,452 Total secured term loan facilities and revolving credit facility $ 628,872 $ 772,190 Less: current portion 81,128 83,352 Secured term loan facilities and revolving credit facility, non-current $ 547,744 $ 688,838 January 2015 Secured Term Loan Facility. This loan facility is secured by first priority mortgages on each of; Navigator Atlas, Navigator Europa, Navigator Oberon, Navigator Triton, Navigator Umbrio, Navigator Centauri, Navigator Ceres, Navigator Ceto Navigator Copernico December 2015 Secured Revolving Credit Facility. . This loan facility is secured by first priority mortgages on each of; Navigator Aurora, Navigator Eclipse, Navigator Nova, Navigator Prominence, Navigator Luga Navigator Yauza October 2016 Secured Term Loan and Revolving Credit Facility. Navigator Jorf This facility is secured by first priority mortgages on each of: Navigator Gemini Navigator Leo, Navigator Libra, Navigator Orion (formerly Navigator Mars) Navigator Neptune Navigator Pegasus Navigator Phoenix Navigator Taurus Navigator Venus Navigator Jorf June 2017 Secured Term Loan and Revolving Credit Facility. ) re-finance The facility is secured by first priority mortgages on each of Navigator Galaxy, Navigator Genesis, Navigator Grace, Navigator Gusto, Navigator Glory, Navigator Capricorn, Navigator Scorpio Navigator Virgo The following table shows the breakdown of secured term loan facilities and total deferred financing costs split between current and non-current December 31, 2016 December 31, 2017 (in thousands) Current Liability Current portion of long-term debt $ (81,128 ) $ (83,352 ) Less: current portion of deferred financing costs 2,664 1,793 Current portion of secured term loan facility, net of deferred financing costs $ (78,464 ) $ (81,559 ) Non-Current Secured term loan facilities net of current portion $ (547,744 ) $ (688,838 ) Less: non-current 7,064 7,180 Non-current non-current $ (540,680 ) $ (681,658 )

Senior Unsecured Bond

Senior Unsecured Bond	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Senior Unsecured Bond	9. Senior Unsecured Bond On February 10, 2017, the Company issued senior unsecured bonds in an aggregate principal amount of $100.0 million with Norsk Tillitsmann ASA as the bond trustee (the “2017 Bonds”). The net proceeds of the issuance of the 2017 Bonds, together with cash on hand, were used to redeem in full all of the Company’s outstanding 9.0% senior unsecured bonds. The 2017 Bonds are governed by Norwegian law and listed on the Nordic ABM which is operated and organized by Oslo Børs ASA. The 2017 Bonds bear interest at a rate of 7.75% per annum and mature on February 10, 2021. Interest is payable semi-annually in arrears on February 10 and August 10. The Company may redeem the 2017 Bonds, in whole or in part, at any time beginning on or after February 11, 2019. Any 2017 Bonds redeemed from February 11, 2019 up until February 10, 2020, are redeemable at 103.875% of par, from February 11, 2020 to August 10, 2020, are redeemable at 101.9375% of par, and from August 11, 2020 to the maturity date are redeemable at 100% of par, in each case, plus accrued interest. The 2017 Bond Agreement contains an option to issue additional bonds up to a maximum issue amount of a further $100.0 million, at identical terms as the original bond issue, except that additional bonds may be issued at a different price. The financial covenants each as defined within the bond agreement are: (a) The issuer shall ensure that the Group (meaning “the Company and its subsidiaries”) maintains a minimum liquidity of the greater of no less than $25.0 million; (b) to maintain an interest coverage ratio (as defined in the bond agreement) of not less than 2.25:1; and (c) maintain a Group equity ratio of minimum 30% (as defined in the bond agreement); At December 31, 2017, the Company was in compliance with all covenants contained in this credit facility. The 2017 Bond Agreement provides that we may declare dividends so long as such dividends do not exceed 50% of our cumulative consolidated net profits after taxes since June 30, 2016. The 2017 Bond Agreement also limits us and our subsidiaries from, among other things, entering into mergers and divestitures, engaging in transactions with affiliates or incurring any additional liens which would have a material adverse effect. In addition, the 2017 Bond Agreement includes customary events of default, including those relating to a failure to pay principal or interest, a breach of covenant, false representation and warranty, a cross-default to other indebtedness, the occurrence of a material adverse effect, or our insolvency or dissolution. The following table shows the breakdown of our senior unsecured bond and total deferred financing costs at December 31, 2017 and December 31 2016: December 31, 2016 December 31, 2017 (in thousands) Senior Unsecured Bond Total Bond $ (125,000 ) $ (100,000 ) Less deferred financing costs — 1,416 Total Bond, net of deferred financing costs $ (125,000 ) $ (98,584 )

Earnings per Share

Earnings per Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings per Share	10. Earnings per Share Basic and diluted earnings per share is calculated by dividing the net income available to common stockholders by the average number of common shares outstanding during the periods. Diluted earnings per share is calculated by adjusting the net income available to common stockholders and the weighted average number of common shares used for calculating basic earnings per share for the effects of all potentially dilutive shares. The calculation of both basic and diluted number of weighted average outstanding shares of: December 31, December 31, December 31, Net income available to common stockholders (in thousands) 98,094 44,638 5,310 Basic weighted average number of shares 55,360,004 55,418,626 55,508,974 Effect of dilutive potential share options: 346,100 375,855 372,480 Diluted weighted average number of shares 55,706,104 55,794,481 55,881,454

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	11. Share-Based Compensation During 2008, the Company’s Board adopted the 2008 Restricted Stock Plan (the “2008 Plan”), which entitled officers, employees, consultants and directors of the Company to receive grants of restricted stock of the Company’s common stock. This 2008 Plan is administered by the Board or a committee of the Board. A holder of restricted stock, awarded under the Plan, shall have the same voting and dividend rights as the Company’s other common stockholders in relation to those shares. Prior to closing of the Company’s initial public offering in November 2013, this 2008 Plan was frozen such that new awards will no longer be issued thereunder. However, any outstanding awards issued prior to the 2008 Plan being frozen shall continue to remain outstanding and extend beyond the date the 2008 Plan was frozen. Any future equity incentive awards will be granted under the new 2013 Long Term Incentive Plan (the “2013 Plan”) entered into prior to the closing of the Company’s initial public offering. The 2013 Plan is administered by the Compensation Committee with certain decisions subject to approval of our Board. The maximum aggregate number of common shares that may be delivered pursuant to options or restricted stock awards granted under the 2013 Plan is 3,000,000 shares of common stock. A holder of restricted stock, awarded under the 2013 Plan, shall have the same voting and dividend rights as the Company’s other common stockholders in relation to those shares. Share awards On March 23, 2017, the Company granted 28,194 restricted shares under the 2013 Plan to non-employee During the year ended December 31, 2017, 22,782 shares that were previously granted under the 2013 Plan to non-employee On March 29, 2016, the Company granted 22,782 shares under the 2013 Plan non-employee During the year ended December 31, 2016, 118,971 shares that were previously granted under the 2008 Plan at a weighted average grant value of $11.10 vested at a fair value of $1,893,223. Restricted share grant activity for the year ended December 31, 2016 and 2017 was as follows: Number of non- vested restricted shares Weighted average grant date fair value Weighted average remaining contractual term Aggregate intrinsic value Balance as of January 1, 2016 121,471 $ 11.28 0.29 years $ 1,658,079 Granted 72,620 15.80 Vested (118,971 ) 11.10 Balance as of December 31, 2016 75,120 $ 15.93 1.59 years $ 698,616 Granted 93,675 12.77 Vested (25,282 ) 16.17 Balance as of December 31, 2017 143,513 13.82 1.49 years $ 1,413,603 Using the straight-line method of expensing the restricted stock grants, the weighted average estimated value of the shares calculated at the date of grant is recognized as compensation cost in the Statement of Income over the period to the vesting date. During the year ended December 31, 2017, the Company recognized $859,061 in share-based compensation costs relating to share grants (year ended December 31, 2016: $636,324). As of December 31, 2017, there was a total of $1,027,683 unrecognized compensation costs relating to the expected future vesting of share-based awards (December 31, 2016: $690,514) which are expected to be recognized over a weighted average period of 1.49 years (December 31, 2016: 1.59 years). Share options Share options issued under the 2013 Plan are not exercisable until the third anniversary of the grant date and can be exercised up to the tenth anniversary of the date of grant. The fair value of each option is calculated on the date of grant based on the Black-Scholes valuation model using the assumptions listed in the table below. Expected volatilities are based on the historic volatility of the Company’s stock price and other factors. The Company does not currently pay dividends and it is assumed this will not change. The expected term of the options granted is anticipated to occur in the range between 4 and 6.5 years. The risk-free rate is the rate adopted from the U.S. Government Zero Coupon Bond. The movements in the existing share options during the years ended December 31, 2016 and 2017 were as follows: Options Number of non- options Weighted average exercise price per share Weighted average remaining contractual term years Aggregate intrinsic value Balance as of January 1, 2016 378,440 21.52 8.35 — Forfeited during the year (4,700 ) 20.09 — — Balance as of December 31, 2016 373,740 $ 21.54 7.70 — Forfeited during the period (5,000 ) 23.85 — — Vested (214,055 ) — — — Balance as of December 31, 2017 154,685 21.87 6.70 $ — On April 14, 2017, 194,055 share options granted on April 14, 2014 at an option price of $24.29 became exercisable. On October 14, 2017, 20,000 share options granted on October 14, 2014 at an option price of $23.18 became exercisable. None of the options were exercised as of December 31, 2017. During the year ended December 31, 2017, the Company recognized $553,894 in share-based compensation costs relating to options granted under the 2013 Plan, recognized in general and administrative costs (year ended December 31, 2016, $937,647). At December 31, 2017, there was $85,898 of total unrecognized compensation costs related to non-vested

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	12. Commitments and Contingencies The contractual obligations schedule set forth below summarizes our contractual obligations as of December 31, 2017. 2018 2019 2020 2021 2022 Thereafter Total (in thousands) Secured term loan facilities and revolving credit facilities 83,352 70,600 128,725 60,600 302,461 126,452 772,190 7.75% senior unsecured bond issue — — — 100,000 — — 100,000 Office operating leases 1,134 1,558 1,345 1,192 115 — 5,344 Total contractual obligations $ 84,486 $ 72,158 $ 130,070 $ 161,792 $ 302,576 $ 126,452 $ 877,534 The Company occupies office space in London with a lease that commenced in January 2017 for a period of 10 years with a mutual break option in January 2022, which is the fifth anniversary from the lease commencement date. The gross rent per year is approximately $1.1 million. The Company entered into a lease for office space in New York commencing on June 1, 2017 and expires on May 31, 2020 to replace an expiring lease. The annual gross rent under this lease is approximately $0.4 million, subject to certain adjustments. The lease term for our representative office in Gdynia, Poland is for a period of five years commencing from April 2017. The gross rent per year is approximately $60,000.

Concentration of Credit Risks

Concentration of Credit Risks	12 Months Ended
	Dec. 31, 2017
Risks and Uncertainties [Abstract]
Concentration of Credit Risks	13. Concentration of Credit Risks The Company’s vessels are chartered under either a time charter arrangement or voyage charter arrangement. Under a time charter arrangement, no security is provided for the payment of charter hire. However, payment is usually required monthly in advance. Under a voyage charter arrangement, a lien may sometimes be placed on the cargo to secure the payment of the accounts receivable, as permitted by the prevailing charter party agreement. At December 31, 2017, 21 of the Company’s 38 operated vessels, were subject to time charters, 11 of which will expire within one year, five which will expire within three years, and five which will expire within ten years. The committed charter income as of December 31, 2017 is as follows: (in thousands) 2018: $ 111,929 2019: $ 89,819 2020: $ 77,876 2021: $ 61,830 2022: $ 62,124 During 2017, five charterers contributed 64.6% of the operating revenue, comprising 16.5%, 16.3%, 11.9%, 10.4% and 9.5% (2016: five charterers contributed 51.4% of the operating revenue, comprising 14.0%, 11.7%, 9.1%, 8.3% and 8.3%). At December 31, 2017 and 2016, all of the Company’s cash and cash equivalents and short-term investments were held by large financial institutions, highly rated by a recognized rating agency.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	14. Income Taxes Navigator Holdings Ltd and its vessel owning subsidiaries are incorporated in the Marshall Islands and under the laws of the Marshall Islands are not subject to tax on income or capital gains and no Marshall Islands withholding tax will be imposed on dividends paid by the Company to its stockholders. 2015 2016 2017 Net Income $ 98,094 $ 44,638 $ 5,310 Tax expense at statutory rate $ — $ — $ — Total statutory tax charge $ — $ — $ — Tax charge in UK subsidiaries $ 383 $ 669 $ 221 Tax credit in Polish subsidiary $ (21 ) $ — $ (130 ) Tax charge in Singapore subsidiary $ 438 $ 508 $ 306 Total Tax charge $ 800 $ 1,177 $ 397

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	15. Subsequent Events On January 31, 2018, the Company entered into a 50/50 joint venture with Enterprise Products Partners L.P. to build a new ethylene export facility along the U.S. Gulf Coast that will have the capacity to export approximately one million tons of ethylene per year. Refrigerated storage for 30,000 tons of ethylene will be constructed on-site

Summary of Significant Accoun24

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Basis of Presentation	(a) Basis of Presentation The consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). The accompanying consolidated financial statements include the accounts of the Company and its subsidiaries (See Note 7) and a Variable Interest Entity (“VIE”). All intercompany accounts and transactions have been eliminated in consolidation. As of December 31, 2017 the Company has consolidated 100% of PT Navigator Khatulistiwa, a VIE for which the Company is deemed to be the primary beneficiary, i.e. it has a controlling financial interest in this entity. The Company owns 49% of the VIE’s common stock, all of its secured debt and has voting control. All economic interests in the residual net assets reside with the Company. A VIE is an entity that in general does not have equity investors with voting rights or that has equity investors that do not provide sufficient financial resources for the entity to support its activities. A controlling financial interest in a VIE is present when a company has the power to direct the activities of a VIE that most significantly impact the entity’s economic performance and has the right to residual gains or the obligation to absorb losses that could potentially be significant to the VIE. During the year ended December 31, 2017, the Company adopted Accounting Standards Update (“ASU”) 2015-17, During the year ended December 31, 2017, the Company adopted ASU 2016-09,
Impairment of Vessels	(d) Impairment of Vessels Our vessels are reviewed for impairment when events or circumstances indicate the carrying amount of the vessel may not be recoverable. When such indicators are present, a vessel is tested for recoverability and we recognize an impairment loss if the sum of the future cash flows (undiscounted and excluding interest charges that will be recognized as an expense when incurred) expected to be generated by the vessel over its estimated remaining useful life are less than its carrying value. If we determine that a vessel’s undiscounted cash flows are less than its carrying value, we record an impairment loss equal to the amount by which its carrying amount exceeds its fair value. The new lower cost basis would result in a lower annual depreciation than before the impairment. Considerations in making such an impairment evaluation include comparison of current carrying values to anticipated future operating cash flows, expectations with respect to future operations and other relevant factors. The estimates and assumptions regarding expected cash flows require considerable judgment and are based upon historical experience, financial forecasts and industry trends and conditions.
Drydocking Costs	(e) Drydocking Costs Each vessel is required to be dry-docked dry-dockings dry-docking. dry-docking dry-docking
Cash and Cash Equivalents	(f) Cash and Cash Equivalents The Company considers highly liquid investments, such as time deposits and certificates of deposit, with an original maturity of three months or less when purchased, to be cash equivalents. The Company has cash in a U.S. financial institution which is insured by the Federal Deposit Insurance Corporation (“FDIC”) for up to $0.3 million. At December 31, 2017 and 2016 and for the years then ended, the Company had balances in this financial institution in excess of the insured amount. The Company also maintains cash balances in foreign financial institutions which are not covered by the FDIC.
Short-Term Investments	(g) Short-Term Investments Short-term investments represent funds deposited in money market funds with an original maturity of more than three months when purchased. The Company records its short-term investments at fair value. Fair value is a market-based measurement that is determined based on assumptions that market participants would use in pricing an asset or a liability. The fair value hierarchy also requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The Company’s short-term investments are classified within Level 1 of the fair value hierarchy.
Accounts Receivable, net	(h) Accounts Receivable, net The Company carries its accounts receivable at cost less an allowance for doubtful accounts. At December 31, 2017 and 2016, the Company evaluated its accounts receivable and established an allowance for doubtful accounts, based on a history of past write-offs, collections and current credit conditions. The Company does not generally charge interest on past-due past-due
Bunkers and lubricant oils	(i) Bunkers and lubricant oils Bunkers and lubricant oils include bunkers (fuel), for those vessels under voyage charter, and lubricants. Under a time charter, the cost of bunkers is borne by and remains the property of the charterer. Bunkers and lubricant oils are accounted for on a first in, first out basis and are valued at cost.
Deferred Finance Costs	j) Deferred Finance Costs Costs incurred in connection with obtaining secured term loan facilities, revolving credit facilities and bonds are recorded as deferred financing costs and are amortized to interest expense over the estimated duration of the related debt. Such costs include fees paid to the lenders or on the lenders’ behalf and associated legal and other professional fees. Under the Accounting Standards Update (ASU) 2015- 03, Interest—Imputation of Interest the Company has adopted the accounting standard (Subtopic 835-30)—simplifying
Deferred Income	(k) Deferred Income Deferred income is the balance of cash received in excess of revenue earned under a time charter or voyage charter arrangement as of the balance sheet date.
Revenue Recognition	(l) Revenue Recognition The Company employs its vessels on time charters, voyage charters or COA’s. With time charters, the Company receives a fixed charter hire per on-hire
Other Comprehensive Income / (Loss)	(m) Other Comprehensive Income / (Loss) The Company follows the provisions of ASC Topic 220 “Comprehensive Income,” which requires separate presentation of certain transactions, which are recorded directly as components of stockholders’ equity. Comprehensive income is comprised of net income and foreign currency translation gains and losses.
Voyage Expenses and Vessel Operating Expenses	(n) Voyage Expenses and Vessel Operating Expenses When the Company employs its vessels on time charter, it is responsible for all the operating expenses of the vessels, such as crew costs, stores, insurance, repairs and maintenance. In the case of voyage charters, the vessel is contracted only for a voyage between two or more ports, and the Company pays for all voyage expenses in addition to the vessel operating expenses. Voyage expenses consist mainly of in port expenses and bunker (fuel) consumption and are recognized as incurred.
Repairs and Maintenance	(o) Repairs and Maintenance All expenditures relating to routine maintenance and repairs are expensed when incurred.
Insurance	(p) Insurance The Company maintains hull and machinery insurance, war risk insurance, protection and indemnity insurance coverage, increased value insurance, demurrage and defense insurance coverage in amounts considered prudent to cover normal risks in the ordinary course of its operations. Premiums paid in advance to insurance companies are recognized as prepaid expenses and recorded as a vessel operating expense over the period covered by the insurance contract. In addition, the Company maintains Directors and Officers insurance.
Share-Based Compensation	(q) Share-Based Compensation The Company records as an expense in its financial statements the fair value of all equity-settled stock-based compensation awards. The terms and vesting schedules for share-based awards vary by type of grant. Generally, the awards vest subject to time-based (immediate to five years) service conditions. Compensation expense is recognized ratably over the service period.
Critical Accounting Estimates	(r) Critical Accounting Estimates The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ materially from these estimates.
Foreign Currency Transactions	(s) Foreign Currency Transactions Substantially all of the Company’s cash receipts are in U.S. Dollars. The Company’s disbursements, however, are in the currency invoiced by the supplier. The Company remits funds in the various currencies invoiced. The non U.S. Dollar invoices received, and their subsequent payments, are converted into U.S. Dollars when the transactions occur. The movement in exchange rates between these two dates is transferred to an exchange difference account and is expensed each month. The exchange risk resulting from these transactions is not material.
Income Taxes	(t) Income Taxes Navigator Holdings Ltd. and its Marshall Islands subsidiaries are currently not required to pay income taxes in the Marshall Islands on ordinary income or capital gains as they qualify as exempt companies. The Company has four subsidiaries incorporated in the United Kingdom where the base tax rate is 19%. One UK subsidiary earns management and other fees from fellow subsidiary companies. The second UK subsidiary holds an investment in our VIE and has a loan to our group subsidiary in Poland. The third subsidiary earns management fees from fellow subsidiary companies. The fourth subsidiary was dormant as at December 31, 2017. The Company has a subsidiary in Poland where the base tax rate is 19%. The Company has a subsidiary incorporated in Singapore where the base tax rate is 17%. The subsidiary earns management and other fees and receives interest from its VIE, PT Navigator Khatulistiwa, The Company considered the income tax disclosure requirements of ASC Topic 740 “Income Taxes,” with regard to disclosing material unrecognized tax benefits; none were identified. The Company’s policy is to recognize accrued interest and penalties for unrecognized tax benefits as a component of tax expense. At December 31, 2017 and 2016, there were no accrued interest and penalties for unrecognized tax benefits.
Earnings Per Share	(u) Earnings Per Share Basic earnings per common share (“Basic EPS”) is computed by dividing the net income available to common stockholders by the weighted-average number of shares outstanding. Diluted earnings per common share (“Diluted EPS”) are computed by dividing the net income available to common stockholders by the weighted average number of common shares and dilutive common share equivalents then outstanding. Shares granted pursuant to the 2013 Restricted Stock Plan are the only dilutive shares, and these shares have been considered as outstanding since their respective grant dates for purposes of computing diluted earnings per share.
Segment Reporting	(v) Segment Reporting Although separate vessel financial information is available, Management internally evaluates the performance of the enterprise as a whole and not on the basis of separate business units or different types of charters. As a result, the Company has determined that it operates as one reportable segment. Since the Company’s vessels regularly move between countries in international waters over many trade routes, it is impractical to assign revenues or earnings from the transportation of international LPG and petrochemical products by geographic area.
Recent Accounting Pronouncements	(w) Recent Accounting Pronouncements The following accounting standards issued as of December 31, 2017, may affect the future financial reporting by Navigator Holdings Ltd: In May 2014, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2014-09, The effective date for ASU 2014-09 2015-14 During the last year the Company has taken part in a series of discussions with a collective of global shipping companies, to ensure key industry specifics have been considered, as well as to consider the differing views within the industry in order to give maximum consideration to the implementation of the new standard. The Company has assessed the potential impact that the adoption of this guidance will have on its financial statements and footnote disclosures, as well as understanding the implications for the company’s internal processes, systems and controls. The adoption of this standard will have little or no impact on the timing or amounts of revenue recognized for our vessels that operate on time charters. For vessels undertaking voyage charters or contracts of affreightment, we determined that the period over which revenue is recognized will change as a result of adopting this standard. The current policy recognizes revenue beginning from the later of the previous discharge port or the charter party date across the period to the date discharge is completed. Under the new standard, revenue will be recognized beginning from load port across the period to the date discharge is complete, reducing the period of time over which revenue is recognized. The Company has calculated that the effect of this change would result in an increase in the amount of revenue earned and recognized for the year ended December 31, 2017 by a net of $ 0.5 million. The adoption of the new revenue recognition standard will also have an impact on related voyage expenses as certain costs incurred to fulfill a contract or performance obligation can be deferred and amortized over the period of the voyage. The Company has calculated that the effect of this change would result in a reduction in the amount of voyage expenses recognized in the financial statements for the year ended December 31, 2017 by a net of $0.2 million. The Company has also considered the impact on reporting under ASC 606 and has adapted its internal processes and controls to reflect the changes. The Company is also considering the impact on Time Charter Equivalent or “TCE”, a non-GAAP In February 2016, the FASB issued ASU 2016-02, on-balance 2016-02 2016-02 not-for-profit 2016-02 In June 2016, the FASB issued ASU 2016–13, Financial Instruments – Credit Losses, which changes the recognition model for the impairment of financial instruments, including accounts receivable, loans and held-to-maturity In August 2016, the FASB issued ASU 2016-15, • Debt prepayment or debt extinguishment costs; • Settlement of zero-coupon • Contingent consideration payments made after a business combination; • Proceeds from the settlement of insurance claims; • Proceeds from the settlement of corporate-owned life insurance policies, including bank-owned life insurance policies; • Distributions received from equity method investees; • Beneficial interests in securitization transactions; and • Separately identifiable cash flows and application of the predominance principle. This ASU is effective for public business entities for annual and interim periods in fiscal years beginning after December 15, 2017. For all other entities, the ASU is effective for annual periods in fiscal years beginning after December 15, 2018. The Company will adopt this standard beginning January 1, 2018. The impact of adopting this ASU will be immaterial to the financial statements. In November 2016, the FASB issued ASU 2016-18,
Vessels In Operation [Member]
Vessels	(b) Vessels in Operation The cost of the vessels (excluding the estimated initial drydocking cost) less their estimated residual value is depreciated on a straight-line basis over the vessel’s estimated economic life. Management estimates the useful life of each of the Company’s vessels to be 30 years from the date of its original construction.
Vessels Under Construction [Member]
Vessels	(c) Vessels Under Construction Vessels under construction are stated at cost, which includes the cost of construction, capitalized interest and other direct costs attributable to the construction. No provision for depreciation is made on construction in progress until such time as the relevant assets are completed and put into use.

Fair Value of Financial Instr25

Fair Value of Financial Instruments Not Accounted For at Fair Value (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, All Other Investments [Abstract]
Schedule of Estimated Fair Value and Carrying Value of Assets and Liabilities Measured at Fair Value on Recurring Basis, Non-recurring Basis	The following table includes the estimated fair value and carrying value of those assets and liabilities. The table excludes accounts receivable, the insurance debtor recoverable and accounts payable. December 31, 2016 December 31, 2017 Fair Value Hierarchy Level Fair Carrying Fair Value Carrying Fair Value (in thousands) Cash and cash equivalents Level 1 57,272 57,272 62,109 62,109 Senior unsecured bond (note 9) Level 2 (125,000 ) (127,423 ) (100,000 ) (96,775 ) Secured term loan facilities and revolving credit facility (note 8) Level 3 (628,872 ) (553,346 ) (772,191 ) (636,220 )

Vessels (Tables)

Vessels (Tables)	12 Months Ended
	Dec. 31, 2017
Vessels Under Construction [Member]
Vessels	2016 2017 Vessels under construction at January 1 $ 170,776 $ 150,492 Payments to shipyard 221,532 174,131 Other payments including initial stores and site costs 12,580 4,783 Capitalized interest 5,067 1,715 Transfer to vessels in operation (259,463 ) (331,121 ) Vessels under construction at December 31 $ 150,492 $ —
Vessels In Operation [Member]
Vessels	Vessel Drydocking Total Cost December 31, 2015 $ 1,462,136 $ 26,729 $ 1,488,865 Additions 10,176 9,902 20,078 Transfer in from vessels under construction 256,663 2,800 259,463 Disposals — (5,482 ) (5,482 ) Reduction in contract cost of newbuild vessels (1,484 ) — (1,484 ) December 31, 2016 1,727,491 33,949 1,761,440 Additions 1,940 268 2,208 Transfer in from vessels under construction 327,571 3,550 331,121 Disposals — (1,492 ) (1,492 ) Reduction in contract cost of newbuild vessels (280 ) — (280 ) December 31, 2017 2,056,722 36,275 2,092,997 Accumulated Depreciation December 31, 2015 $ 215,024 $ 9,390 $ 224,414 Charge for the period 53,653 8,496 62,149 Disposals for the period — (5,482 ) (5,482 ) December 31, 2016 268,677 12,404 281,081 Charge for the period 64,031 9,238 73,269 Disposals for the period — (1,492 ) (1,492 ) December 31, 2017 332,708 20,150 352,858 Net Book Value December 31, 2015 $ 1,247,112 $ 17,339 $ 1,264,451 December 31, 2016 $ 1,458,814 $ 21,545 $ 1,480,359 December 31, 2017 $ 1,724,014 $ 16,125 $ 1,740,139

Group Subsidiaries (Tables)

Group Subsidiaries (Tables)	12 Months Ended
	Dec. 31, 2017
Schedule of Investments [Abstract]
Group Subsidiaries	At December 31, 2017 and 2016, the company had the following significant subsidiaries: Corporation Name Percentage Ownership as of December 31, Country of Incorporation Subsidiary of Limited Liability Company 2016 2017 - Navigator Gas US L.L.C. 100 % 100 % Delaware (USA) Service company - Navigator Gas L.L.C. 100 % 100 % Marshall Islands Holding company ~ Navigator Aries 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Atlas L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Aurora L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Centauri L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Ceres L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Ceto L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Copernico L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Capricorn L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Eclipse L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Europa L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Galaxy L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Gemini L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Genesis L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Glory L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Grace L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Gusto L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Jorf L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Leo L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Libra L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Luga L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Magellan L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Mars L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Neptune L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Nova L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Oberon L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Pegasus L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Phoenix L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Prominence L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Saturn L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Scorpio L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Taurus L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Triton L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Umbrio L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Venus L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Virgo L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ Navigator Yauza L.L.C. 100 % 100 % Marshall Islands Vessel-owning company ~ NGT Services (UK) Ltd 100 % 100 % England Service company ~ NGT Services (Poland) Sp. Z O.O 100 % 100 % Poland Service company ~ Navigator Gas Ship Management Ltd. 100 % 100 % England Service company ~ Falcon Funding PTE Ltd 100 % 100 % Singapore Service company ~ Navigator Gas Invest Ltd 100 % 100 % England Investment company - PT Navigator Khatulistiwa 49 % 49 % Indonesia Vessel-owning company ~ Navigator Terminals L.L.C. n/a * 100 % Marshall Islands Investment company ~ Navigator Terminals Invest Ltd n/a * 100 % England Investment company - Navigator Ethylene Terminals L.L.C. n/a * 100 % Delaware (USA) Investment company - Enterprise Navigator Ethylene Terminal L.L.C. n/a * 50 % Texas (USA) Terminal operator * Entities formed during 2017.

Secured Term Loan Facilities 28

Secured Term Loan Facilities and Revolving Credit Facility (Tables)	12 Months Ended
	Dec. 31, 2017
Schedule of Annual Principal Payments to Term Loans and Revolving Credit Facilities	The table below represents the annual principal payments to be made under our term loans and revolving credit facilities after December 31, 2017: December 31, December 31, Due within one year $ 81,128 $ 83,352 Due in two years 188,586 70,600 Due in three years 41,823 128,725 Due in four years 99,948 60,600 Due in five years 31,823 302,461 Due in more than five years 185,564 126,452 Total secured term loan facilities and revolving credit facility $ 628,872 $ 772,190 Less: current portion 81,128 83,352 Secured term loan facilities and revolving credit facility, non-current $ 547,744 $ 688,838
Schedule of Breakdown of Secured Term Loan Facilities and Total Deferred Financing Costs Split Between Current and Non-Current Liabilities	The following table shows the breakdown of secured term loan facilities and total deferred financing costs split between current and non-current December 31, 2016 December 31, 2017 (in thousands) Current Liability Current portion of long-term debt $ (81,128 ) $ (83,352 ) Less: current portion of deferred financing costs 2,664 1,793 Current portion of secured term loan facility, net of deferred financing costs $ (78,464 ) $ (81,559 ) Non-Current Secured term loan facilities net of current portion $ (547,744 ) $ (688,838 ) Less: non-current 7,064 7,180 Non-current non-current $ (540,680 ) $ (681,658 )
2017 Senior Unsecured Bonds [Member]
Schedule of Breakdown of Secured Term Loan Facilities and Total Deferred Financing Costs Split Between Current and Non-Current Liabilities	The following table shows the breakdown of our senior unsecured bond and total deferred financing costs at December 31, 2017 and December 31 2016: December 31, 2016 December 31, 2017 (in thousands) Senior Unsecured Bond Total Bond $ (125,000 ) $ (100,000 ) Less deferred financing costs — 1,416 Total Bond, net of deferred financing costs $ (125,000 ) $ (98,584 )

Earnings per Share (Tables)

Earnings per Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Calculation of Basic and Diluted Number of Weighted Average Outstanding Shares	The calculation of both basic and diluted number of weighted average outstanding shares of: December 31, December 31, December 31, Net income available to common stockholders (in thousands) 98,094 44,638 5,310 Basic weighted average number of shares 55,360,004 55,418,626 55,508,974 Effect of dilutive potential share options: 346,100 375,855 372,480 Diluted weighted average number of shares 55,706,104 55,794,481 55,881,454

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Restricted Share Grant Activity	Restricted share grant activity for the year ended December 31, 2016 and 2017 was as follows: Number of non- vested restricted shares Weighted average grant date fair value Weighted average remaining contractual term Aggregate intrinsic value Balance as of January 1, 2016 121,471 $ 11.28 0.29 years $ 1,658,079 Granted 72,620 15.80 Vested (118,971 ) 11.10 Balance as of December 31, 2016 75,120 $ 15.93 1.59 years $ 698,616 Granted 93,675 12.77 Vested (25,282 ) 16.17 Balance as of December 31, 2017 143,513 13.82 1.49 years $ 1,413,603
Summary of Stock Option Activity	The movements in the existing share options during the years ended December 31, 2016 and 2017 were as follows: Options Number of non- options Weighted average exercise price per share Weighted average remaining contractual term years Aggregate intrinsic value Balance as of January 1, 2016 378,440 21.52 8.35 — Forfeited during the year (4,700 ) 20.09 — — Balance as of December 31, 2016 373,740 $ 21.54 7.70 — Forfeited during the period (5,000 ) 23.85 — — Vested (214,055 ) — — — Balance as of December 31, 2017 154,685 21.87 6.70 $ —

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Summary of Contractual Obligations	The contractual obligations schedule set forth below summarizes our contractual obligations as of December 31, 2017. 2018 2019 2020 2021 2022 Thereafter Total (in thousands) Secured term loan facilities and revolving credit facilities 83,352 70,600 128,725 60,600 302,461 126,452 772,190 7.75% senior unsecured bond issue — — — 100,000 — — 100,000 Office operating leases 1,134 1,558 1,345 1,192 115 — 5,344 Total contractual obligations $ 84,486 $ 72,158 $ 130,070 $ 161,792 $ 302,576 $ 126,452 $ 877,534

Concentration of Credit Risks (

Concentration of Credit Risks (Tables)	12 Months Ended
	Dec. 31, 2017
Risks and Uncertainties [Abstract]
Committed Charter Income	The committed charter income as of December 31, 2017 is as follows: (in thousands) 2018: $ 111,929 2019: $ 89,819 2020: $ 77,876 2021: $ 61,830 2022: $ 62,124

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Summary of Income Tax Reconciliation	However, the Company’s UK, Polish and Singaporean subsidiaries are subject to local taxes. 2015 2016 2017 Net Income $ 98,094 $ 44,638 $ 5,310 Tax expense at statutory rate $ — $ — $ — Total statutory tax charge $ — $ — $ — Tax charge in UK subsidiaries $ 383 $ 669 $ 221 Tax credit in Polish subsidiary $ (21 ) $ — $ (130 ) Tax charge in Singapore subsidiary $ 438 $ 508 $ 306 Total Tax charge $ 800 $ 1,177 $ 397

Description of Business - Addit

Description of Business - Additional Information (Detail)	Dec. 31, 2017Vesselm³
Schedule Of Description Of Business [Line Items]
Number of gas carriers owned & operated	38
Semi Refrigerated [Member]
Schedule Of Description Of Business [Line Items]
Number of gas carriers owned & operated	31
Fully Refrigerated [Member]
Schedule Of Description Of Business [Line Items]
Number of gas carriers owned & operated	7
Minimum [Member]
Schedule Of Description Of Business [Line Items]
Gas carrier cargo capacity | m³	20,085
Maximum [Member]
Schedule Of Description Of Business [Line Items]
Gas carrier cargo capacity | m³	38,000

Summary of Significant Accoun35

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017USD ($)Company
Summary Of Significant Accounting Policies [Line Items]
Variable Interest Entity, consolidated	100.00%
Share based compensation, vesting period	5 years
UNITED KINGDOM [Member]
Summary Of Significant Accounting Policies [Line Items]
Base Tax rate	19.00%
Number of subsidiaries | Company	4
POLAND [Member]
Summary Of Significant Accounting Policies [Line Items]
Base Tax rate	19.00%
SINGAPORE [Member]
Summary Of Significant Accounting Policies [Line Items]
Base Tax rate	17.00%
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Dry dock period	60 months
Cash in a U.S. financial institution, insured by the Federal Deposit Insurance Corporation	$ 300,000
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Dry dock period	30 months
Vessels Under Construction [Member]
Summary Of Significant Accounting Policies [Line Items]
Construction in progress- Depreciation provision	$ 0
Accounting Standards Update 2014-09 [Member]
Summary Of Significant Accounting Policies [Line Items]
Increase in revenue due to adoption of new standard	500,000
Reduction in voyage expense due to adoption of new standard	$ (200,000)
Common Stock [Member]
Summary Of Significant Accounting Policies [Line Items]
Variable Interest Entity, consolidated	49.00%
Vessel [Member]
Summary Of Significant Accounting Policies [Line Items]
Useful life of vessels	30 years

Fair Value of Financial Instr36

Fair Value of Financial Instruments Not Accounted For at Fair Value - Additional Information (Detail)	Dec. 31, 2017	Feb. 10, 2017	Dec. 31, 2016	Dec. 31, 2015
2017 Senior Unsecured Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate on bond	7.75%	7.75%	7.75%	7.75%

Fair Value of Financial Instr37

Fair Value of Financial Instruments Not Accounted For at Fair Value - Schedule of Estimated Fair Value and Carrying Value of Assets and Liabilities Measured at Fair Value on Recurring Basis, Non-recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, Carrying Amount Asset	$ 62,109	$ 57,272	$ 87,779	$ 62,526
Senior unsecured bond, Carrying Amount (Liability)	(100,000)	(125,000)
Secured term loan facilities and revolving credit facility, Carrying Amount (Liability)	(772,190)	(628,872)
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents, Fair Value Asset	62,109	57,272
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior unsecured bond, Fair Value (Liability)	(96,775)	(127,423)
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Secured term loan facilities and revolving credit facility, Fair Value (Liability)	$ (636,220)	$ (553,346)

Accounts Receivable Net - Addit

Accounts Receivable Net - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Accounts Receivable, Net [Abstract]
Provision for doubtful accounts	$ 0.3	$ 0.2

Vessel in Operation - Vessels (

Vessel in Operation - Vessels (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Net Book Value, ending balance	$ 1,611	$ 194
Vessels In Operation [Member]
Property, Plant and Equipment [Line Items]
Cost, beginning balance	1,761,440	1,488,865
Cost, Additions	2,208	20,078
Cost, Transfer in from vessels under construction	331,121	259,463
Cost, Disposals	(1,492)	(5,482)
Cost, Reduction in contract cost of newbuild vessels	(280)	(1,484)
Cost, ending balance	2,092,997	1,761,440
Accumulated Depreciation, beginning balance	281,081	224,414
Accumulated Depreciation, Charge for the period	73,269	62,149
Accumulated Depreciation, Disposals for the period	(1,492)	(5,482)
Accumulated Depreciation, ending balance	352,858	281,081
Net Book Value, ending balance	1,740,139	1,480,359	$ 1,264,451
Vessels In Operation [Member] | Vessel [Member]
Property, Plant and Equipment [Line Items]
Cost, beginning balance	1,727,491	1,462,136
Cost, Additions	1,940	10,176
Cost, Transfer in from vessels under construction	327,571	256,663
Cost, Reduction in contract cost of newbuild vessels	(280)	(1,484)
Cost, ending balance	2,056,722	1,727,491
Accumulated Depreciation, beginning balance	268,677	215,024
Accumulated Depreciation, Charge for the period	64,031	53,653
Accumulated Depreciation, ending balance	332,708	268,677
Net Book Value, ending balance	1,724,014	1,458,814	1,247,112
Vessels In Operation [Member] | Drydocking [Member]
Property, Plant and Equipment [Line Items]
Cost, beginning balance	33,949	26,729
Cost, Additions	268	9,902
Cost, Transfer in from vessels under construction	3,550	2,800
Cost, Disposals	(1,492)	(5,482)
Cost, ending balance	36,275	33,949
Accumulated Depreciation, beginning balance	12,404	9,390
Accumulated Depreciation, Charge for the period	9,238	8,496
Accumulated Depreciation, Disposals for the period	(1,492)	(5,482)
Accumulated Depreciation, ending balance	20,150	12,404
Net Book Value, ending balance	$ 16,125	$ 21,545	$ 17,339

Vessel in Operation - Additiona

Vessel in Operation - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)Vessel	Dec. 31, 2016USD ($)Vessel	Dec. 31, 2015USD ($)
Property, Plant and Equipment [Line Items]
Payment for property plant and equipment	$ 1,940	$ 1,733	$ 3,348
Property, plant and equipment, net	$ 1,611	$ 194
Semi Refrigerated [Member]
Property, Plant and Equipment [Line Items]
Refrigerated gas carrier, acquired | Vessel		2
Payment for property plant and equipment		$ 243,800
Semi Refrigerated [Member] | Midsize Carrier [Member]
Property, Plant and Equipment [Line Items]
Refrigerated gas carrier, acquired | Vessel	2
Payment for property plant and equipment	$ 156,800
Semi Refrigerated [Member] | Handysize Carrier [Member]
Property, Plant and Equipment [Line Items]
Refrigerated gas carrier, acquired | Vessel	2
Payment for property plant and equipment	$ 152,500
Semi Refrigerated [Member] | Ethylene Carrier [Member]
Property, Plant and Equipment [Line Items]
Refrigerated gas carrier, acquired | Vessel		2
Fully Refrigerated [Member] | Liquefied Gas Carriers [Member]
Property, Plant and Equipment [Line Items]
Refrigerated gas carrier, acquired	1
Collateralized Loan Obligations [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	$ 1,591,000

Vessels Under Construction (Det

Vessels Under Construction (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Vessels under construction at January 1	$ 150,492
Payments to shipyard	180,629	$ 239,179	$ 236,648
Vessels under construction at December 31		150,492
Vessels Under Construction [Member]
Property, Plant and Equipment [Line Items]
Vessels under construction at January 1	150,492	170,776
Other payments including initial stores and site costs	4,783	12,580
Capitalized interest	1,715	5,067
Transfer to vessels in operation	(331,121)	(259,463)
Vessels under construction at December 31		150,492	$ 170,776
Vessels Under Construction [Member] | Shipyard [Member]
Property, Plant and Equipment [Line Items]
Payments to shipyard	$ 174,131	$ 221,532

Group Subsidiaries - Group Subs

Group Subsidiaries - Group Subsidiaries (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
PT Navigator Khatulistiwa [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	49.00%	49.00%
Country of Incorporation	Indonesia
Subsidiary of Limited Liability Company	Vessel-owning company
Enterprise Navigator Ethylene Terminal L.L.C [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	50.00%
Country of Incorporation	Texas (USA)
Subsidiary of Limited Liability Company	Terminal operator
Navigator Gas US L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Delaware (USA)
Subsidiary of Limited Liability Company	Service company
Navigator Gas L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Holding company
Navigator Aries L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Atlas L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Aurora LLC [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Centauri LLC [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Ceres L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Ceto L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Copernico L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Capricorn L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Eclipse LLC [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Europa L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Galaxy L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Gemini L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Genesis L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Glory L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Grace L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Gusto L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Jorf L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Leo L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Libra L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Luga L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Magellan L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Mars L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Neptune L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Nova LLC [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Oberon L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Pegasus L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Phoenix L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Prominence L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Saturn L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Scorpio L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Taurus L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Triton L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Umbrio L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Venus L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Virgo L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
Navigator Yauza L.L.C. [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Vessel-owning company
NGT Services (UK) Ltd [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	England
Subsidiary of Limited Liability Company	Service company
NGT Services (Poland) Sp. Z O.O [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Poland
Subsidiary of Limited Liability Company	Service company
Navigator Gas Ship Management Ltd [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	England
Subsidiary of Limited Liability Company	Service company
Falcon Funding PTE Ltd [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	Singapore
Subsidiary of Limited Liability Company	Service company
Navigator Gas Invest Ltd [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%	100.00%
Country of Incorporation	England
Subsidiary of Limited Liability Company	Investment company
Navigator Terminals LLC [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%		[1]
Country of Incorporation	Marshall Islands
Subsidiary of Limited Liability Company	Investment company
Navigator Terminals Invest Ltd [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%		[1]
Country of Incorporation	England
Subsidiary of Limited Liability Company	Investment company
Navigator Ethylene Terminals L.L.C [Member]
Subsidiary or Equity Method Investee [Line Items]
Percentage Ownership	100.00%		[1]
Country of Incorporation	Delaware (USA)
Subsidiary of Limited Liability Company	Investment company
[1]	Entities formed during 2017.

Group Subsidiaries - Additional

Group Subsidiaries - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Subsidiary or Equity Method Investee [Line Items]
Total assets	$ 1,853,887	$ 1,724,843
Total liabilities	890,674	768,363
Variable Interest Entity, Primary Beneficiary [Member]
Subsidiary or Equity Method Investee [Line Items]
Total assets	132,200	137,500
Total liabilities	$ 54,400	$ 73,000

Secured Term Loan Facilities 44

Secured Term Loan Facilities and Revolving Credit Facility - Schedule of Annual Principal Payments to Term Loans and Revolving Credit Facilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Maturities of Long-term Debt [Abstract]
Due within one year	$ 83,352	$ 81,128
Due in two years	70,600	188,586
Due in three years	128,725	41,823
Due in four years	60,600	99,948
Due in five years	302,461	31,823
Due in more than five years	126,452	185,564
Total secured term loan facilities and revolving credit facility	772,190	628,872
Less: current portion	83,352	81,128
Secured term loan facilities and revolving credit facility, non-current portion	688,838	547,744
Total secured term loan facilities and revolving credit facility	$ 772,190	$ 628,872

Secured Term Loan Facilities 45

Secured Term Loan Facilities and Revolving Credit Facility - Additional Information (Detail)	Oct. 28, 2016USD ($)	Dec. 31, 2015USD ($)	Jan. 27, 2015USD ($)	Dec. 31, 2017USD ($)Payments	Dec. 31, 2015USD ($)	Jun. 30, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2014USD ($)
Debt Instrument [Line Items]
Cash balance required		$ 87,779,000		$ 62,109,000	$ 87,779,000		$ 57,272,000	$ 62,526,000
April 2013 Loan Facility [Member]
Debt Instrument [Line Items]
Credit facility, refinancing			$ 120,000,000
January 2015 Secured Term Loan Facility [Member]
Debt Instrument [Line Items]
Credit facility term			7 years	7 years
Credit facility, maximum borrowing capacity			$ 278,100,000
Credit facility, amount outstanding				$ 222,300,000
Credit facility, number of repayments | Payments				4
Debt instrument covenant description				The financial covenants each as defined within the credit facility are a) the maintenance at all times of cash and cash equivalents in an amount equal to or greater than (i) $25.0 million and (ii) 5% of the total indebtedness; b) a ratio of EBITDA to interest expense of not less than 31; and c) maintain a ratio of total stockholders' equity to total assets of not less than 30%.
January 2015 Secured Term Loan Facility [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis spread on credit facility interest rate			2.70%
January 2015 Secured Term Loan Facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Credit facility, periodic payment				$ 500,000
Credit facility, final payment				15,600,000
Aggregate fair value of collateral vehicles required for borrowings under facility			135.00%
Cash balance required				$ 25,000,000
Cash required as percent of indebtedness				5.00%
EBITDA to interest expense Ratio				300.00%
Total equity to total assets				30.00%
January 2015 Secured Term Loan Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Credit facility, periodic payment				$ 700,000
Credit facility, final payment				18,300,000
December 2015 Secured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility term		7 years
Credit facility, maximum borrowing capacity		$ 290,000,000			$ 290,000,000
Credit facility, amount outstanding				263,100,000
Credit facility, periodic payment				4,100,000
Credit facility, final payment				$ 185,100,000
Credit facility, number of repayments				19
Debt instrument covenant description				The financial covenants each as defined within the credit facility are: a) the maintenance at all times of cash and cash equivalents in an amount equal to or greater than (i) $25.0 million and (ii) 5 per cent of the total indebtedness; b) a ratio of EBITDA to interest expense of not less than 3:1; and c) maintain a ratio of total stockholders’ equity to total assets of not less than 30%.
Commitment fee on credit facility				0.74%
Credit facility, expiring period					2022-12
Debt payment end date				Dec. 21, 2022
Commitment fee on credit facility				0.74%
December 2015 Secured Revolving Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis spread on credit facility interest rate		2.10%
December 2015 Secured Revolving Credit Facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Aggregate fair value of collateral vehicles required for borrowings under facility					125.00%
Cash balance required				$ 25,000,000
Cash required as percent of indebtedness				5.00%
EBITDA to interest expense Ratio				300.00%
Total equity to total assets				30.00%
October 2016 Secured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility term	7 years
Credit facility, maximum borrowing capacity	$ 220,000,000
Credit facility, final payment				$ 37,800,000
Credit facility, number of repayments				17
Debt instrument covenant description				The financial covenants each as defined within the credit facility are: a) the maintenance at all times of cash and cash equivalents in an amount equal to or greater than (i) $25.0 million and (ii) 5 per cent of the total indebtedness; b) a ratio of EBITDA to interest expense of not less than 3:1; and c) maintain a ratio of total stockholders’ equity to total assets of not less than 30%.
Commitment fee on credit facility				0.91%
Credit facility, expiring period	2023-12
Commitment fee on credit facility				0.91%
Credit facility	$ 130,000,000
Drawdowns under the credit facility				$ 138,100,000
October 2016 Secured Revolving Credit Facility [Member] | Quarterly Installment One [Member]
Debt Instrument [Line Items]
Credit facility, periodic payment				9,400,000
October 2016 Secured Revolving Credit Facility [Member] | Quarterly Installment Two [Member]
Debt Instrument [Line Items]
Credit facility, periodic payment				7,100,000
October 2016 Secured Revolving Credit Facility [Member] | Quarterly Installment Three [Member]
Debt Instrument [Line Items]
Credit facility, periodic payment				7,100,000
October 2016 Secured Revolving Credit Facility [Member] | Quarterly Installment Four [Member]
Debt Instrument [Line Items]
Credit facility, periodic payment				5,500,000
October 2016 Secured Revolving Credit Facility [Member] | Quarterly Installment Five [Member]
Debt Instrument [Line Items]
Credit facility, periodic payment				4,100,000
October 2016 Secured Revolving Credit Facility [Member] | Quarterly Installment Six [Member]
Debt Instrument [Line Items]
Credit facility, periodic payment				1,000,000
October 2016 Secured Revolving Credit Facility [Member] | Quarterly Installment Seven [Member]
Debt Instrument [Line Items]
Credit facility, periodic payment				500,000
October 2016 Secured Revolving Credit Facility [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, amount outstanding	55,000,000
October 2016 Secured Revolving Credit Facility [Member] | Navigator Jorf L.L.C. [Member] | Newbuilding Term Loan [Member]
Debt Instrument [Line Items]
Credit facility, amount outstanding	$ 35,000,000
October 2016 Secured Revolving Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis spread on credit facility interest rate	2.60%
October 2016 Secured Revolving Credit Facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Aggregate fair value of collateral vehicles required for borrowings under facility	125.00%
Cash balance required				$ 25,000,000
Cash required as percent of indebtedness				5.00%
EBITDA to interest expense Ratio				300.00%
Total equity to total assets				30.00%
June 2017 Secured Term Loan Facility [Member] | Navigator Gas L.L.C. [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity				$ 100,000,000
Credit facility, periodic payment				4,100,000
Drawdowns under the credit facility				$ 148,800,000
June 2017 Secured Term Loan and Revolving Credit Facility [Member] | Navigator Gas L.L.C. [Member]
Debt Instrument [Line Items]
Credit facility term				6 years
Credit facility, maximum borrowing capacity				$ 160,800,000		$ 160,800,000
Debt instrument covenant description				The financial covenants each as defined within the credit facility are: a) the maintenance at all times of cash and cash equivalents in an amount equal to or greater than (i) $25.0 million and (ii) 5 per cent of the total indebtedness; b) a ratio of EBITDA to interest expense of not less than 2.5:1; and c) maintain a ratio of total stockholders’ equity to total assets of not less than 30%.
Commitment fee on credit facility				0.91%
Credit facility, expiring period				2023-06
Commitment fee on credit facility				0.91%
Credit facility, amount drawn during period				$ 0
June 2017 Secured Term Loan and Revolving Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Navigator Gas L.L.C. [Member]
Debt Instrument [Line Items]
Basis spread on credit facility interest rate				2.30%
June 2017 Secured Term Loan and Revolving Credit Facility [Member] | Minimum [Member] | Navigator Gas L.L.C. [Member]
Debt Instrument [Line Items]
Aggregate fair value of collateral vehicles required for borrowings under facility				125.00%
Cash balance required				$ 25,000,000
Cash required as percent of indebtedness				5.00%
EBITDA to interest expense Ratio				250.00%
Total equity to total assets				30.00%
February 2013 Secured Term Loan Facility [Member] | Navigator Gas L.L.C. [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity						$ 270,000,000
June 2017 Revolving Credit Facility [Member] | Navigator Gas L.L.C. [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity				$ 60,800,000

Secured Term Loan Facilities 46

Secured Term Loan Facilities and Revolving Credit Facility - Schedule of Breakdown of Secured Term Loan Facilities and Total Deferred Financing Costs Split Between Current and Non-Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current Liability
Current portion of long-term debt	$ (83,352)	$ (81,128)
Less: current portion of deferred financing costs	1,793	2,664
Current portion of secured term loan facility, net of deferred financing costs	(81,559)	(78,464)
Non-Current Liability
Secured term loan facilities net of current portion	(688,838)	(547,744)
Less: non-current portion of deferred financing costs	7,180	7,064
Non-current secured term loan facilities, net of current portion and non-current deferred financing costs	$ (681,658)	$ (540,680)

Senior Unsecured Bond - Additio

Senior Unsecured Bond - Additional Information (Detail) - USD ($)	Feb. 10, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Minimum liquidity to be maintained, amount		$ 62,109,000	$ 57,272,000	$ 87,779,000	$ 62,526,000
2017 Senior Unsecured Bonds [Member]
Debt Instrument [Line Items]
Aggregate principal amount	$ 100,000,000
Interest rate on bond	7.75%	7.75%	7.75%	7.75%
Debt instrument maturity date	Feb. 10, 2021
Debt instrument redemption description		The Company may redeem the 2017 Bonds, in whole or in part, at any time beginning on or after February 11, 2019. Any 2017 Bonds redeemed from February 11, 2019 up until February 10, 2020, are redeemable at 103.875% of par, from February 11, 2020 to August 10, 2020, are redeemable at 101.9375% of par, and from August 11, 2020 to the maturity date are redeemable at 100% of par, in each case, plus accrued interest.
Additional bonds issuance option, maximum amount		$ 100,000,000
Debt instrument covenant description		The financial covenants each as defined within the bond agreement are: (a) The issuer shall ensure that the Group (meaning “the Company and its subsidiaries”) maintains a minimum liquidity of the greater of no less than $25.0 million; (b) to maintain an interest coverage ratio (as defined in the bond agreement) of not less than 2.25:1; and (c) maintain a Group equity ratio of minimum 30% (as defined in the bond agreement); At December 31, 2017, the Company was in compliance with all covenants contained in this credit facility.
2017 Senior Unsecured Bonds [Member] | February 11, 2019 through February 10, 2020 [Member]
Debt Instrument [Line Items]
Debt instrument redeemable percentage	103.875%
2017 Senior Unsecured Bonds [Member] | February 11, 2020 through August 10, 2020 [Member]
Debt Instrument [Line Items]
Debt instrument redeemable percentage	101.9375%
2017 Senior Unsecured Bonds [Member] | August 11, 2020 through Maturity Date [Member]
Debt Instrument [Line Items]
Debt instrument redeemable percentage	100.00%
Interest payment description on bond		Interest is payable semi-annually in arrears on June 18 and December 18.
2012 Senior Unsecured Bonds [Member]
Debt Instrument [Line Items]
Interest rate on bond	9.00%	9.00%	9.00%	9.00%
7.75% Senior Unsecured Bond [Member] | Minimum [Member]
Debt Instrument [Line Items]
Minimum liquidity to be maintained, amount		$ 25,000,000
Interest coverage ratio		225.00%
Gross Equity ratio		30.00%
7.75% Senior Unsecured Bond [Member] | Maximum [Member]
Debt Instrument [Line Items]
Dividend payable percentage		50.00%

Senior Unsecured Bond - Schedul

Senior Unsecured Bond - Schedule of Breakdwn of Senior Unsecured Bond and Total Deferred Financig Costs (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Total Bond, net of deferred financing costs	$ (772,190)	$ (628,872)
2017 Senior Unsecured Bonds [Member]
Debt Instrument [Line Items]
Total Bond	(100,000)	(125,000)
Less deferred financing costs	1,416
Total Bond, net of deferred financing costs	$ (98,584)	$ (125,000)

Earnings per Share - Calculatio

Earnings per Share - Calculation of Basic and Diluted Number of Weighted Average Outstanding Shares (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income available to common stockholders (in thousands)	$ 5,310	$ 44,638	$ 98,094
Basic weighted average number of shares	55,508,974	55,418,626	55,360,004
Effect of dilutive potential share options:	372,480	375,855	346,100
Diluted weighted average number of shares	55,881,454	55,794,481	55,706,104

Share-Based Compensation - Addi

Share-Based Compensation - Additional Information (Detail) - USD ($)	Oct. 14, 2017	Apr. 14, 2017	Mar. 23, 2017	Mar. 29, 2016	Mar. 17, 2015	Oct. 14, 2014	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock unit, vesting in period							25,282	118,971
Weighted average grant value per share, vested							$ 16.17	$ 11.10
Share vested, total fair value								$ 1,893,223
Share-based compensation costs							$ 859,061	636,324
Vesting period							5 years
Options, vesting in period	20,000	194,055					214,055
Grant date option price, vested	$ 23.18	$ 24.29
Exercised, number of shares							0
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)					4 years	4 years
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)					6 years 6 months	6 years 6 months
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation cost not yet recognized							$ 1,027,683	$ 690,514
Total compensation cost not yet recognized period for recognition							1 year 5 months 27 days	1 year 7 months 2 days
2013 Long Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares authorized for grant							3,000,000
Vesting term							Shares under the 2013 Plan non-employee directors with a weighted average value of $15.80 per share. These shares vest on the first anniversary of the grant date.
Total compensation cost not yet recognized							$ 85,898	$ 673,022
2013 Long Term Incentive Plan [Member] | Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation cost not yet recognized period for recognition							2 months 16 days	8 months 12 days
2013 Long Term Incentive Plan [Member] | General and Administrative Costs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation costs							$ 553,894	$ 937,647
Non Employee Director [Member] | 2013 Long Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Number of shares			28,194	22,782
Weighted average value, per share			$ 12.77	$ 15.80
Vesting term							Shares under the 2013 Plan to non-employee directors with a weighted average value of $12.77 per share. These restricted shares vest on the first anniversary of the grant date.
Restricted stock unit, vesting in period							22,782
Weighted average grant value per share, vested							$ 15.80
Share vested, total fair value							$ 305,279
Chief Executive Officer [Member] | 2013 Long Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Number of shares			42,023	29,966
Weighted average value, per share			$ 12.77	$ 15.80
Officers and Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period							3 years
Share-based Compensation, expiration period							10 years
Officers and Employees [Member] | 2013 Long Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Number of shares			23,458	19,872
Weighted average value, per share			$ 12.77	$ 15.80
Officer [Member] | 2013 Long Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock unit, vesting in period							2,500
Weighted average grant value per share, vested							$ 19.59
Share vested, total fair value							$ 24,888

Share-Based Compensation - Rest

Share-Based Compensation - Restricted Share Grant Activity (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of RSUs
Unvested, beginning balance	75,120	121,471
Granted	93,675	72,620
Vested	(25,282)	(118,971)
Unvested, ending balance	143,513	75,120	121,471
Weighted-average grant date fair value
Unvested, beginning balance	$ 15.93	$ 11.28
Granted	12.77	15.80
Vested	16.17	11.10
Unvested, ending balance	$ 13.82	$ 15.93	$ 11.28
Weighted-average remaining contractual terms (Years)
Weighted-average remaining contractual terms (Years)	1 year 5 months 27 days	1 year 7 months 2 days	3 months 15 days
Aggregated intrinsic value
Aggregated intrinsic value	$ 1,413,603	$ 698,616	$ 1,658,079

Share-Based Compensation - Summ

Share-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($)	Oct. 14, 2017	Apr. 14, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Beginning Balance			373,740	378,440
Options
Forfeited during the period			(5,000)	(4,700)
Vested	(20,000)	(194,055)	(214,055)
Ending Balance			154,685	373,740	378,440
Beginning Balance			$ 21.54	$ 21.52
Weighted-Average Exercise Price
Forfeited during the period			23.85	$ 20.09
Weighted-Average Remaining Contractual Term (years)
Vested			$ 0
Beginning Balance			6 years 8 months 12 days	7 years 8 months 12 days	8 years 4 months 6 days
Ending Balance			$ 21.87	$ 21.54	$ 21.52
Aggregate Intrinsic Value			$ 0	$ 0	$ 0

Commitments and Contingencies -

Commitments and Contingencies - Summary of Contractual Obligations (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Contractual Obligation Fiscal Year Maturity [Line Items]
2,018	$ 83,352	$ 81,128
2,019	70,600	188,586
2,020	128,725	41,823
2,021	60,600	99,948
2,022	302,461	31,823
Thereafter	126,452	185,564
Total	772,190	628,872
2,018	84,486
2,019	72,158
2,020	130,070
2,021	161,792
2,022	302,576
Thereafter	126,452
Total	877,534
Secured Term Loan Facilities and Revolving Credit Facilities [Member]
Contractual Obligation Fiscal Year Maturity [Line Items]
2,018	83,352
2,019	70,600
2,020	128,725
2,021	60,600
2,022	302,461
Thereafter	126,452
Total	772,190
2017 Senior Unsecured Bonds [Member]
Contractual Obligation Fiscal Year Maturity [Line Items]
2,021	100,000
Total	98,584	$ 125,000
Office Operating Leases [Member]
Contractual Obligation Fiscal Year Maturity [Line Items]
2,018	1,134
2,019	1,558
2,020	1,345
2,021	1,192
2,022	115
Thereafter	0
Total	$ 5,344

Commitments and Contingencies54

Commitments and Contingencies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017USD ($)
London [Member]
Schedule Of Commitments And Contingencies [Line Items]
Lease term	10 years
Lease term, mutual break clause	5 years
Operating lease future minimum payment per year	$ 1,100,000
NEW YORK [Member]
Schedule Of Commitments And Contingencies [Line Items]
Operating lease future minimum payment per year	$ 400,000
Lease expiration date	May 31, 2020
POLAND [Member]
Schedule Of Commitments And Contingencies [Line Items]
Lease term	5 years
Operating lease future minimum payment per year	$ 60,000

Concentration of Credit Risks -

Concentration of Credit Risks - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017ItemVessel	Dec. 31, 2016Item
Concentration Risk [Line Items]
Company's operated vessels (Including)chartered-in vessel	21
Product Concentration Risk [Member] | Sales Revenue, Net [Member]
Concentration Risk [Line Items]
Percentage of operating revenue	64.60%	51.40%
Number of charterers | Item	5	5
Product Concentration Risk [Member] | One Time Charter [Member] | Sales Revenue, Net [Member]
Concentration Risk [Line Items]
Percentage of operating revenue	16.50%	14.00%
Product Concentration Risk [Member] | Two Time Charter [Member] | Sales Revenue, Net [Member]
Concentration Risk [Line Items]
Percentage of operating revenue	16.30%	11.70%
Product Concentration Risk [Member] | Three Time Charter [Member] | Sales Revenue, Net [Member]
Concentration Risk [Line Items]
Percentage of operating revenue	11.90%	9.10%
Product Concentration Risk [Member] | Four Time Charter [Member] | Sales Revenue, Net [Member]
Concentration Risk [Line Items]
Percentage of operating revenue	10.40%	8.30%
Product Concentration Risk [Member] | Five Time Charter [Member] | Sales Revenue, Net [Member]
Concentration Risk [Line Items]
Percentage of operating revenue	9.50%	8.30%
Time Charter [Member]
Concentration Risk [Line Items]
Company's operated vessels (Including)chartered-in vessel	38
Time Charter [Member] | One Year [Member]
Concentration Risk [Line Items]
Company's operated vessels (Including)chartered-in vessel	11
Time Charter [Member] | Three Year Term [Member]
Concentration Risk [Line Items]
Company's operated vessels (Including)chartered-in vessel	5
Time Charter [Member] | Ten Year Term [Member]
Concentration Risk [Line Items]
Company's operated vessels (Including)chartered-in vessel	5

Concentration of Credit Risks56

Concentration of Credit Risks - Committed Charter Income (Detail) - Fair Value, Concentration of Risk, Market Risk Management, Effects on Income or Net Assets [Member] - Time Charter [Member] $ in Thousands	Dec. 31, 2017USD ($)
Concentration Risk [Line Items]
2018:	$ 111,929
2019:	89,819
2020:	77,876
2021:	61,830
2022:	$ 62,124

Income Taxes - Summary of Incom

Income Taxes - Summary of Income Tax Reconciliation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
Net income	$ 5,310	$ 44,638	$ 98,094
Tax expense at statutory rate	0	0	0
Total statutory tax charge	0	0	0
Total Tax charge	397	1,177	800
UNITED KINGDOM [Member]
Income Tax Contingency [Line Items]
Total Tax charge	221	669	383
POLAND [Member]
Income Tax Contingency [Line Items]
Total Tax charge	(130)		(21)
SINGAPORE [Member]
Income Tax Contingency [Line Items]
Total Tax charge	$ 306	$ 508	$ 438

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - 50/50 Joint Venture With Enterprise Products Partners L.P [Member] - Ethylene Carrier [Member] - Subsequent Event [Member]	Jan. 31, 2018TMT
Subsequent Event [Line Items]
Exporting capacity per year | MT	1
Production capacity per hour	1,000
Refrigerated [Member]
Subsequent Event [Line Items]
Storage capacity	30,000