ICON Public Limited (ICLR) 20-F 27 Feb 20 2019 FY Annual report (foreign) Financial data

Document and Entity Information

Document and Entity Information Document	12 Months Ended
	Dec. 31, 2019shares
Entity Addresses [Line Items]
Document Type	20-F
Document Registration Statement	false
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
Document Transition Report	false
Document Shell Company Report	false
Entity File Number	333-08704
Entity Registrant Name	ICON PLC
Entity Incorporation, State or Country Code	L2
Entity Address, Address Line One	South County Business Park,
Entity Address, Address Line Two	Leopardstown,
Entity Address, City or Town	Dublin 18,
Entity Address, Country	IE
Title of 12(b) Security	ORDINARY SHARES, PAR VALUE €0.06 EACH
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding	53,622,206
Entity Well Known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filler Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Document Accounting Standard	U.S. GAAP
Entity Shell Company	false
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
No Trading Symbol Flag	true
Entity Central Index Key	0001060955
Current Fiscal Year End Date	--12-31
Entity Address, Postal Zip Code	D18 X5R3
Business Contact
Entity Addresses [Line Items]
Entity Address, Address Line One	South County Business Park
Entity Address, Address Line Two	Leopardstown
Entity Address, City or Town	Dublin 18
Entity Address, Country	IE
Contact Personnel Name	Brendan Brennan
Contact Personnel Email Address	Brendan.Brennan@iconplc.com
Country Region	353
City Area Code	1
Local Phone Number	291-2000
Entity Address, Postal Zip Code	D18 X5R3

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current Assets:
Cash and cash equivalents	$ 520,309	$ 395,851
Available for sale investments (Note 3a)	49,628	59,910
Accounts receivable, net (Note 17)	527,708	414,791
Unbilled revenue (Note 17)	422,769	362,926
Other receivables	39,290	40,459
Prepayments and other current assets	41,517	36,801
Income taxes receivable (Note 13)	23,759	19,445
Total current assets	1,624,980	1,330,183
Other Assets:
Property, plant and equipment, net (Note 6)	165,087	158,669
Goodwill (Note 4)	883,170	756,260
Operating right-of-use assets (Note 22)	104,977
Other non-current assets	17,439	14,525
Non-current income taxes receivable (Note 13)	17,230	20,023
Non-current deferred tax asset (Note 13)	16,682	13,577
Investments in equity-long term (Note 3b)	10,053	6,963
Intangible assets (Note 5)	67,894	54,055
Total Assets	2,907,512	2,354,255
Current Liabilities:
Accounts payable	24,050	13,288
Unearned revenue (Note 17)	366,988	274,468
Other liabilities (Note 7)	378,543	317,143
Income taxes payable (Note 13)	12,031	5,724
Current bank credit lines and loan facilities (Note 23)	349,640	0
Total current liabilities	1,131,252	610,623
Other Liabilities:
Non-current bank credit lines and loan facilities (Note 23)	0	349,264
Non-current operating lease liabilities (Note 22)	76,593
Non-current other liabilities (Note 8)	17,512	13,446
Non-current government grants (Note 11)	813	877
Non-current income taxes payable (Note 13)	14,301	17,551
Non-current deferred tax liability (Note 13)	9,476	8,213
Commitments and contingencies (Note 15)	0	0
Total Liabilities	1,249,947	999,974
Shareholders' Equity:
Ordinary shares, par value 6 euro cents per share; 100,000,000 shares authorized, (Note 12), 53,622,206 shares issued and outstanding at December 31, 2019 and 53,971,706 shares issued and outstanding at December 31, 2018.	4,635	4,658
Additional paid-in capital	577,961	529,642
Other undenominated capital (Note 12 (a))	1,052	983
Accumulated other comprehensive income (Note 21)	(75,819)	(69,328)
Retained earnings	1,110,226	888,326
Total Shareholders’ Equity	1,618,055	1,354,281
Redeemable noncontrolling interest	39,510	0
Total Shareholders' Equity and Redeemable Noncontrolling Interest	1,657,565	1,354,281
Total Liabilities and Shareholders’ Equity and Redeemable Noncontrolling Interest	$ 2,907,512	$ 2,354,255

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - € / shares	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Ordinary shares, par value (in EUR per share)	€ 0.06	€ 0.06
Ordinary shares, shares authorized (in shares)	100,000,000	100,000,000
Ordinary shares, shares issued (in shares)	53,622,206	53,971,706
Ordinary shares, shares outstanding (in shares)	53,622,206	53,971,706

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue:
Gross revenue	$ 2,805,839,000	$ 2,595,777,000	$ 2,402,321,000
Reimbursable expenses	0	0	(643,882,000)
Total revenue	2,805,839,000	2,595,777,000	1,758,439,000
Costs and expenses:
Selling, general and administrative	336,748,000	325,794,000	323,741,000
Depreciation and amortization	61,550,000	65,916,000	61,297,000
Restructuring (Note 14)	0	12,490,000	7,753,000
Total costs and expenses	2,372,433,000	2,222,420,000	1,420,101,000
Income from operations	433,406,000	373,357,000	338,338,000
Interest income	6,859,000	4,759,000	2,346,000
Interest expense	(13,276,000)	(13,502,000)	(12,627,000)
Income before income taxes expense	426,989,000	364,614,000	328,057,000
Income tax expense (Note 13)	(51,133,000)	(41,958,000)	(46,569,000)
Net Income	375,856,000	322,656,000	281,488,000
Net income attributable to noncontrolling interest	(1,870,000)	0	0
Net income attributable to the Group	$ 373,986,000	$ 322,656,000	$ 281,488,000
Net income per Ordinary Share attributable to the Group (Note 26):
Basic (dollars per share)	$ 6.85	$ 5.96	$ 5.20
Diluted (dollars per share)	$ 6.79	$ 5.89	$ 5.13
Weighted average number of ordinary shares outstanding:
Basic (in shares)	53,859,537	54,118,764	54,129,439
Diluted (in shares)	54,333,461	54,790,663	54,849,046
Direct Costs
Costs and expenses:
Direct costs	$ 1,974,135,000	$ 1,818,220,000	$ 1,027,310,000

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 375,856	$ 322,656	$ 281,488
Other comprehensive income, net of tax
Currency translation adjustment	(1,313)	(26,522)	33,966
Currency impact of long-term funding	(2,710)	(4,834)	13,730
Unrealized capital gain/(loss) – investments	681	(155)	(272)
Actuarial (loss)/gain on defined benefit pension plan	(2,226)	2,855	50
Amortization of interest rate hedge	(923)	(923)	(923)
Fair value of cash flow hedge	0	(1,036)	1,036
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	369,365	292,041	329,075
Less comprehensive income attributable to redeemable noncontrolling interest	(1,870)	0	0
Total comprehensive income	$ 367,495	$ 292,041	$ 329,075

Consolidated Statements of Shar

Consolidated Statements of Shareholders' Equity and Comprehensive Income - USD ($) $ in Thousands	Total	Ordinary Shares	Additional Paid-in Capital	Other Undenominated Capital	Accumulated Other Comprehensive Income	Retained Earnings	Redeemable Noncontrolling Interest
Beginning balance (in shares) at Dec. 31, 2016		54,530,843
Beginning balance at Dec. 31, 2016	$ 945,174	$ 4,692	$ 438,126	$ 809	$ (86,300)	$ 587,847
Comprehensive Income:
Net income	281,488					281,488
Currency translation adjustment	33,966				33,966
Currency impact of long-term funding	13,730				13,730
Unrealized capital loss - investments	(272)				(272)
Actuarial (loss)/gain on defined benefit pension plan	50				50
Amortization of interest rate hedge	(923)				(923)
Fair value of cash flow hedge	1,036				1,036
Total comprehensive income	329,075
Exercise of share options (in shares)		458,243
Exercise of share options	13,906	$ 31	13,875
Issue of restricted share units / performance share units (in shares)		681,742
Issue of restricted share units / performance share units	44	$ 44
Share based compensation expense	29,351		29,351
Share issue costs	(15)		(15)
Repurchase of ordinary shares (in shares)		(1,589,227)
Repurchase of ordinary shares	(133,106)	$ (103)		103		(133,106)
Share repurchase costs	(106)					(106)
Ending balance (in shares) at Dec. 31, 2017		54,081,601
Ending balance at Dec. 31, 2017	1,191,000	$ 4,664	481,337	912	(38,713)	742,800
Beginning balance at Dec. 31, 2016							$ 0
Ending balance at Dec. 31, 2017							0
Comprehensive Income:
Net income	322,656					322,656
Currency translation adjustment	(26,522)				(26,522)
Currency impact of long-term funding	(4,834)				(4,834)
Unrealized capital loss - investments	(155)				(155)
Actuarial (loss)/gain on defined benefit pension plan	2,855				2,855
Amortization of interest rate hedge	(923)				(923)
Fair value of cash flow hedge	(1,036)				(1,036)
Total comprehensive income	292,041
Exercise of share options (in shares)		408,699
Exercise of share options	16,806	$ 29	16,777
Issue of restricted share units / performance share units (in shares)		489,568
Issue of restricted share units / performance share units	36	$ 36
Share based compensation expense	31,544		31,544
Share issue costs	(16)		(16)
Repurchase of ordinary shares (in shares)		(1,008,162)
Repurchase of ordinary shares	(128,960)	$ (71)		71		(128,960)
Share repurchase costs	$ (66)					(66)
Ending balance (in shares) at Dec. 31, 2018	53,971,706	53,971,706
Ending balance at Dec. 31, 2018	$ 1,354,281	$ 4,658	529,642	983	(69,328)	888,326
Ending balance at Dec. 31, 2018	0						0
Comprehensive Income:
Net income	373,986					373,986
Currency translation adjustment	(1,313)				(1,313)
Currency impact of long-term funding	(2,710)				(2,710)
Unrealized capital loss - investments	681				681
Actuarial (loss)/gain on defined benefit pension plan	(2,226)				(2,226)
Amortization of interest rate hedge	(923)				(923)
Fair value of cash flow hedge	0
Total comprehensive income	367,495
Exercise of share options (in shares)		329,870
Exercise of share options	21,621	$ 22	21,599
Issue of restricted share units / performance share units (in shares)		355,730
Issue of restricted share units / performance share units	24	$ 24
Share based compensation expense	26,733		26,733
Share issue costs	(13)		(13)
Repurchase of ordinary shares (in shares)		(1,035,100)
Repurchase of ordinary shares	(146,931)	$ (69)		69		(146,931)
Share repurchase costs	(107)					(107)
Noncontrolling interest adjustment to redemption amount	$ (5,048)
Ending balance (in shares) at Dec. 31, 2019	53,622,206	53,622,206
Ending balance at Dec. 31, 2019	$ 1,618,055	$ 4,635	$ 577,961	$ 1,052	$ (75,819)	$ 1,110,226
Increase (Decrease) in Temporary Equity [Roll Forward]
Net income							1,870
Acquisition of redeemable noncontrolling interest							32,592
Noncontrolling interest adjustment to redemption amount							5,048
Ending balance at Dec. 31, 2019	$ 39,510						$ 39,510

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended			24 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
Cash flows from operating activities:
Net income	$ 375,856	$ 322,656	$ 281,488
Adjustments to reconcile net income to net cash provided by operating activities:
Loss on disposal of property, plant and equipment	346	70	228
Depreciation expense	45,603	50,565	43,436
Amortization of operating right-use-assets	30,372
Amortization of intangibles	15,947	15,351	17,861
Amortization of government grants	(44)	(47)	(44)
Interest on short term investments	(1,065)	(1,329)	(1,088)
Realized gain on sale of short term investments	(55)	(56)	(112)
Interest on operating lease liability	2,626
Loss/(gain) on re-measurement of financial assets	800	(800)	0
Amortization of gain on interest rate hedge	(923)	(923)	(923)
Amortization of financing costs	540	812	556
Stock compensation expense	26,819	31,594	30,573
Deferred tax (benefit)/expense	(1,537)	1,652	10,729
Changes in assets and liabilities:
(Increase)/decrease in accounts receivable	(101,545)	(37,557)	57,747
Increase in unbilled revenue	(55,790)	(98,510)	(62,491)
Decrease in other receivables	2,513	3,107	1,771
(Increase)/decrease in prepayments and other current assets	(3,583)	(3,237)	4,359
(Increase)/decrease in other non-current assets	(2,912)	856	(1,524)
Increase/(decrease) in unearned revenue	86,567	(6,253)	(7,174)
Increase in other current liabilities	19,864	2,009	6,679
Decrease in operating lease liabilities	(33,437)
Increase/(decrease) in other non-current liabilities	1,405	(1,034)	(3,710)
Increase/(decrease) in income taxes payable	734	(5,220)	(2,293)
Increase/(decrease) in accounts payable	3,440	(5,067)	7,014
Net cash provided by operating activities	412,541	268,639	383,082
Cash flows from investing activities:
Purchase of property, plant and equipment	(50,645)	(48,397)	(44,717)
Purchase of subsidiary undertakings	(131,272)	(1,645)	(144,131)
Cash acquired with subsidiary undertaking	11,697	0	19,649
Sale of available for sale investments	21,686	99,865	33,086
Purchase of available for sale investments	(9,603)	(80,956)	(41,701)
Purchase of investments in equity - long term	(3,890)	(6,163)	0	$ (10,100)
Net cash used in investing activities	(162,027)	(37,296)	(177,814)
Cash flows from financing activities:
Financing costs	0	(823)	0
Proceeds from the exercise of equity compensation	21,645	16,842	13,950
Share issue costs	(13)	(16)	(15)
Repurchase of ordinary shares	(146,931)	(128,960)	(133,106)
Share repurchase costs	(107)	(66)	(106)
Net cash used in financing activities	(125,406)	(113,023)	(119,277)
Effect of exchange rate movements on cash	(650)	(5,328)	4,327
Net increase in cash and cash equivalents	124,458	112,992	90,318
Cash and cash equivalents at beginning of year	395,851	282,859	192,541	282,859
Cash and cash equivalents at end of year	$ 520,309	$ 395,851	$ 282,859	$ 520,309

Description of Business

Description of Business	12 Months Ended
	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	Description of business ICON plc and its subsidiaries ("the Company" or "ICON") is a clinical research organization ("CRO"), providing outsourced development services on a global basis to the pharmaceutical, biotechnology and medical device industries. We specialize in the strategic development, management and analysis of programs that support all stages of the clinical development process from compound selection to Phase I-IV clinical studies. Our vision is to be the Global CRO partner of choice in drug development by delivering best in class information, solutions and performance in clinical and outcomes research. We believe that we are one of a select group of CROs with the expertise and capability to conduct clinical trials in most major therapeutic areas on a global basis and have the operational flexibility to provide development services on a stand-alone basis or as part of an integrated "full service" solution. At December 31, 2019 we had approximately 14,650 employees, in 97 locations in 40 countries. During the year ended December 31, 2019 , we derived approximately 31.8% , 58.5% and 9.7% of our revenue in the United States, Europe and Rest of World, respectively. We began operations in 1990 and have expanded our business predominately through internal growth, together with a number of strategic acquisitions to enhance our capabilities and expertise in certain areas of the clinical development process. We are incorporated in Ireland and our principal executive office is located at: South County Business Park, Leopardstown, Dublin 18, Republic of Ireland. The contact telephone number of this office is +353 1 2912000.

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Significant Accounting Policies	Significant accounting policies The accounting policies noted below were applied in the preparation of the accompanying financial statements of the Company and are in conformity with accounting principles generally accepted in the United States. (a) Basis of consolidation The consolidated financial statements include the financial statements of the Company and all of its subsidiaries. All significant intercompany profits, transactions and account balances have been eliminated. The results of subsidiary undertakings acquired in the period are included in the Consolidated Statement of Operations from the date of acquisition. (b) Use of estimates The preparation of financial statements in conformity with generally accepted accounting principles in the United States requires management to make estimates and judgments 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 reported period. Actual results could differ from those estimates. The principal management estimates and judgments used in preparing the financial statements relate to revenue recognition and taxation. (c) Revenue recognition The Company primarily earns revenues by providing a number of different services to its customers. These services, which are integral elements of the clinical development process, include clinical trials management, consulting, contract staffing, and laboratory services. Contracts range in duration from a number of months to several years. ASC 606 - Revenue from Contracts with Customers (years ended December 31, 2019 and December 31, 2018) ICON adopted ASC 606 'Revenue from Contracts with Customers ' (ASC 606) standard using the cumulative effect transition method for the first time in the year ended December 31, 2018. Under this transition method, ICON applied the new standard as at the date of initial application (i.e. January 1, 2018), without restatement of comparative amounts. The cumulative effect of initially applying the new standard (to revenue, costs and tax) was recorded as an adjustment to the opening balance of equity at the date of initial application. The comparative information, for the year ended December 31, 2017 is not adjusted and therefore continues to be reported under ASC 605 ‘Revenue Recognition’ (ASC 605) and therefore in accordance with previous accounting policies. The new standard requires application of five steps: (1) identify the contract(s) with a customer; (2) identify the performance obligation in the contract; (3) determine the transaction price; (4) allocate the transaction price to the performance obligations in the contract; and (5) recognize revenue when (or as) the entity satisfies the performance obligation. Clinical trial service revenue The most significant impact of application of the standard relates to our assessment of performance and percentage of completion in respect of our clinical trial service revenue. Prior to application of ASC 606, the revenue attributable to performance was determined based on both input and output methods of measurement on a percentage of completion basis. We have concluded that under the new standard, a clinical trial service is a single performance obligation satisfied over time i.e. the full service obligation in respect of a clinical trial (including those services performed by investigators and other parties) is considered a single performance obligation. Promises offered to the customer are not distinct within the context of the contract. We have concluded that ICON is the contract principal in respect of both direct services and in the use of third parties (principally investigator services) that support the clinical research project. The transaction price is determined by reference to the contract or change order value (total service revenue and pass-through/ reimbursable expenses) adjusted to reflect a realizable contract value. Revenue is recognized as the single performance obligation is satisfied. The progress towards completion for clinical service contracts is measured based on an input measure being total project costs incurred (inclusive of third party costs) at each reporting period as a percentage of total forecast project costs. Contracting services revenue On evaluation of the principles at (1) - (5) set-out above in respect of ASC 606, the Company has availed of the practical expedient which results in recognition of revenue on a right to invoice basis. Application of the practical expedient reflects the right to consideration from the customer in an amount that corresponds directly with the value to the customer of the performance completion to date. This reflects hours performed by contract staff. Consulting services revenue On application of the ASC 606 principles at (1) - (5) set-out above, we have concluded that our consulting services contracts represent a single performance obligation satisfied over time. The transaction price is determined by reference to contract or change order value. Revenue is recognized as the performance obligation is satisfied. The progress towards completion for consulting contracts is measured based on total project inputs (time) at each reporting period. Laboratory services revenue Revenue is recognized when, or as, obligations under the terms of a contract are satisfied, which occurs when control of the products or services are transferred to the customer. Revenue for laboratory services is measured as the amount of consideration we expect to receive in exchange for transferring products or services. Where contracts with customers contain multiple performance obligations, the transaction price is allocated to each performance obligation based on the estimated relative selling price of the promised good or service. Service revenue is recognized over time as the services are delivered to the customer based on the extent of progress towards completion of the performance obligation. The determination of the methodology to measure progress requires judgment and is based on the nature of services provided. This requires an assessment of the transfer of value to the customer. The right to invoice measure of progress is generally related to rate per unit contracts, as the extent of progress towards completion is measured based on discrete service or time-based increments, such as samples tested or labor hours incurred. Revenue is recorded in the amount invoiced since that amounts corresponds to the value of the Company's performance and the transfer of value to the customer. Commissions Incremental costs of obtaining a contract were also considered on adoption of ASC 606. Commission costs of $12 million were recognized as an asset on the Consolidated Balance Sheet on application of ASC 606 in respect of those contracts that exceed one year. Where commission costs relate to contracts that are less than one year, the practical expedient is applied as the amortization period of the asset which would arise on deferral would be one year or less. ASC 605 - Revenue recognition (year ended December 31, 2017) Revenue for services, as rendered, is recognized only after persuasive evidence of an arrangement exists, the sales price is fixed or determinable and collectability is reasonably assured. Clinical trials management revenue is recognized on a proportional performance method. Depending on the contractual terms revenue is either recognized on the percentage of completion method based on the relationship between hours incurred and the total estimated hours of the trial or on the unit of delivery method. Contract costs equate to the product of labor hours incurred and compensation rates. For the percentage of completion method, the input (effort expended) method has been used to measure progress towards completion as there is a direct relationship between input and productivity. Contract revenue is the product of the aggregated labor hours required to complete the specified contract tasks at the agreed contract rates. The Company regularly reviews the estimate of total contract time to ensure such estimates remain appropriate taking into account actual contract stage of completion, remaining time to complete and any identified changes to the contract scope. Remaining time to complete depends on the specific contract tasks, the complexity of the contract and can include geographical site selection and initiation, patient enrollment, patient testing and level of results analysis required. While the Company may routinely adjust time estimates, the Company's estimates and assumptions historically have been accurate in all material respects in the aggregate. Where revenue is recognized on the unit of delivery method, the basis applied is the number of units completed as a percentage of the total number of contractual units. Consulting revenue is recognized on a fee-for-service basis as each hour of the related service is performed. Contract staffing revenue is recognized on a fee-for-service basis, over the time the related service is performed. Laboratory service revenue is recognized on a fee-for-service basis. The Company accounts for laboratory service contracts as multiple element arrangements, with contractual elements comprising laboratory kits and laboratory testing, each of which can be sold separately. Sales prices for contractual elements are determined by reference to objective and reliable evidence of their sales price. Revenues for contractual elements are recognized on the basis of the number of deliverable units completed in the period. License and support fee revenues are recognized rateably over the period of the related agreement. Revenue from software services is recognized using the percentage of completion method based on the relationship between hours incurred and the total estimated hours required to perform the service. Contracts generally contain provisions for renegotiation in the event of changes in the scope, nature, duration, or volume of services of the contract. Renegotiated amounts are recognized as revenue by revision to the total contract value arising as a result of an authorized customer change order. (d) Third party costs (Reimbursable expenses) Reimbursable expenses comprise investigator payments and certain other costs which are reimbursed by clients under terms specific to each contract to the investigators. Third party costs (reimbursable expenses) and the related revenue were separately presented on the face of the Consolidated Statement of Operations for periods up to and including the year ended December 31, 2017. See sections (c) and (e) for accounting policy in respect of the treatment of activity relating to reimbursable expenses on revenue (c) and costs (e) on adoption of ASC 606. (e) Direct costs Direct costs consist of compensation, associated employee benefits and share-based payments for project-related employees and other direct project-related costs. Reimbursable expenses are presented within direct costs. This presentation is to align the presentation of costs with our assessment that our clinical trial service is a single performance obligation satisfied over time i.e. the full service obligation is in respect of a clinical trial (including those services performed by investigators and other parties) is considered a single performance obligation. Reimbursable expenses are recorded once the activity which forms the basis for the cost has occurred. Investigator payment costs are recorded and reported reflecting investigator activity over the life of the contract. Investigator payments are made based on predetermined contractual arrangements. Payments may differ from the recording and reporting of the expense which is based on activity. (f) Advertising costs All costs associated with advertising and promotion are expensed as incurred. The advertising and promotion costs were $8,088,451 , $6,516,637 and $6,744,333 for the years ended December 31, 2019 , December 31, 2018 and December 31, 2017 respectively. (g) Foreign currencies and translation of subsidiaries The Company's financial statements are prepared in United States dollars. Transactions in currencies other than the functional currency of the Company are recorded at the rate ruling at the date of the transaction. Monetary assets and liabilities denominated in currencies other than the functional currency of the Company are translated into the functional currency at exchange rates prevailing at the Balance Sheet date. Adjustments resulting from these translations are charged or credited to income. Amounts charged or credited to the Consolidated Statements of Operations for the years ended December 31, 2019 , December 31, 2018 and December 31, 2017 were as follows: Year ended December 31, 2019 2018 2017 (in thousands) Amounts charged/(credited) $ 590 $ (3,876 ) $ 7,760 The financial statements of subsidiaries with other functional currencies are translated at period end rates for the Consolidated Balance Sheets and average rates for the Consolidated Statements of Operations. Translation gains and losses arising are reported as a movement on accumulated other comprehensive income. Foreign currency transaction gains and losses are reported in other comprehensive income rather than through income where the foreign currency transaction is 'long-term investment' in nature i.e. settlement is not planned or anticipated in the foreseeable future. (h) Disclosure of fair value of financial instruments Cash, cash equivalents, unbilled revenue, other receivables, available for sale investments, prepayments and other current assets, accounts receivable, accounts payable, investigator payments, payments on account/unearned revenue, accrued liabilities, accrued bonuses and income taxes payable have carrying amounts that approximate fair value due to the short term maturities of these instruments. Other liabilities' carrying amounts approximate fair value based on net present value of estimated future cash flows. Debt is measured at historical cost. Financial instruments are measured in the Consolidated Balance Sheets at fair value using a fair value hierarchy of valuation inputs. The hierarchy prioritizes the inputs into three levels based on the extent to which inputs used in measuring fair value are observable in the market. Each fair value measurement is reported in one of three levels, which is determined by the lowest level input that is significant to the fair value measurement in its entirety. These levels are: Level 1: Inputs are based upon unadjusted quoted prices for identical instruments traded in active markets. Level 2: Inputs are based upon quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active and model-based valuation techniques for which all significant assumptions are observable in the market or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3: Inputs are generally unobservable and typically reflect management’s estimates of assumptions that market participants would use in pricing the asset or liability. The Group's Senior notes (private placement debt) is carried at $350.0 million (prior to related financing costs). The carrying value at December 31, 2019 , closely approximates fair value. The Company classifies its investments in short term debt or equity investments as available for sale, as it does not actively trade such securities nor does it intend to hold them to maturity. The fair value of short term investments are represented by level 1 fair value measurements – quoted prices in active markets for identical assets. The unrealized movements in fair value are recognized in equity until disposal or sale, at which time, those unrealized movements from prior periods are recognized in Consolidated Statement of Operations. Losses other than temporary, which reduce the carrying amount below cost are recognized in Consolidated Statement of Operations. (i) Business combinations The cost of a business combination is measured as the aggregate of the fair values at the date of exchange of assets given, liabilities incurred or assumed and equity instruments issued in exchange for control. Where a business combination agreement provides for an adjustment to the cost of the acquisition which is contingent upon future events, the amount of the estimated adjustment is recognized at the acquisition date at the fair value of the contingent consideration. Any changes to this estimate outside the measurement period will depend on the classification of the contingent consideration. If the contingent consideration is classified as equity it shall not be re-measured and the settlement shall be accounted for within equity. If the contingent consideration is classified as a liability any adjustments will be accounted for through the Consolidated Statement of Operations or Other Comprehensive Income depending on whether the liability is considered a financial instrument. The assets, liabilities and contingent liabilities of businesses acquired are measured at their fair values at the date of acquisition. In the case of a business combination which is completed in stages, the fair values of the identifiable assets, liabilities and contingent liabilities are determined at the date of each exchange transaction. When the initial accounting for a business combination is determined provisionally, any subsequent adjustments to the provisional values allocated to the identifiable assets, liabilities and contingent liabilities are made within twelve months of the acquisition date and presented as adjustments to goodwill in the reporting period in which the adjustments are determined. The Company allocates a share of net income to the noncontrolling interest holders based on percentage ownership. ICON acquired a majority ownership interest in MeDiNova. Included in the purchase agreement are put and call option arrangements with the noncontrolling interest holders that require (put option) or enable (call option) ICON to purchase the remaining minority ownership at a future date. The option is accounted for as temporary equity, which is presented separately as redeemable noncontrolling interest on the Consolidated Balance Sheet. This classification reflects the assessment that the instruments are contingently redeemable in accordance with ASC 480-10-S99 'Distinguishing Liabilities from Equity'. Redeemable noncontrolling interests are accreted to their redemption value over the period from the date of issuance to the first date on which the option is exercisable. The change in the option's redemption value is recorded against retained earnings. In a computation of earnings per share, the accretion of redeemable noncontrolling interests to their redemption value is a reduction of net income attributable to the Group. Basic and diluted net income per ordinary share attributable to the Group includes the adjustment to reflect the accretion of the noncontrolling interest to its redemption value. (j) Goodwill and Impairment Goodwill represents the excess of the cost of acquired entities over the net amounts assigned to assets acquired and liabilities assumed. Goodwill primarily comprises acquired workforce in place which does not qualify for recognition as an asset apart from goodwill. Goodwill is stated net of any provision for impairment. The Company tests goodwill annually for any impairments or whenever events occur which may indicate impairment. The Company applied the provisions of ASU 2017-04 'Intangibles - Goodwill and Other: Simplifying the test for goodwill impairment' with effect from January 1, 2018. Under the amendment, the Company was required to perform its annual goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An impairment charge would be recognized for any amount by which the carrying amount exceeds the reporting unit's fair value up to the amount of existing goodwill. The amendment allows an entity to perform a qualitative assessment for a reporting unit to determine if the quantitative impairment test is necessary. No impairment was recognized as a result of the impairment testing carried out for the years ended December 31, 2019 , December 31, 2018 and December 31, 2017 . (k) Intangible assets Intangible assets are amortized on a straight line basis over their estimated useful life. (l) Cash and cash equivalents Cash and cash equivalents include cash and highly liquid investments with initial maturities of three months or less and are stated at cost, which approximates market value. (m) Investments in debt, equity and other Available for sale investments The Company classifies short-term investments as available for sale in accordance with the terms of ASC 320 'Investments - Debt and Equity Securities' . Realized gains and losses are determined using specific identification. The investments are reported at fair value, with unrealized gains or losses reported in a separate component of shareholders' equity. Any differences between the cost and fair value of the investments are represented by accrued interest and unrealized gains/losses. Long term investments The Company classifies its interests in funds having considered the nature of its investment, the extent of influence over operating and financial decisions and the availability of readily determinable fair values. The Company determined that the interests in funds at December 31, 2019 meet the definition of equity securities without readily determinable fair values. Effective from January 1, 2018, the Company concluded that the interests held at December 31, 2018 and December 31, 2019 qualify for the NAV practical expedient in ASC 820 ' Fair value measurements and disclosure s'. Any increases or decreases in fair value are recognized in net income in the period. These are therefore measured at Level 3 of the fair value hierarchy. (n) Accounts receivable, net Accounts receivable are recorded at fair value less an allowance for doubtful accounts. The allowance is an estimate based on historical collection experience, current economic and market conditions, and a review of the current status of each customer's trade accounts receivable. Account balances are written-off against the allowance when the Group determines that it is probable that the receivable will not be recovered. Where the Company enters into an agreement to sell certain portfolios of its accounts receivable balances, the sale is accounted for in accordance with ASC Topic 860 'Transfers and Servicing' (ASC 860). Agreements which result in true sales of the transferred receivables, as defined in ASC 860, which occur when receivables are transferred without recourse to ICON, are excluded from amounts reported in the Consolidated Balance Sheet. Cash proceeds received from such sales are included in operating cash flows. The associated finance costs are presented as interest expense. (o) Inventory Inventory is valued at the lower of cost and net realizable value and after provisions for obsolescence. The cost of inventories comprises the purchase price and attributable costs, less trade discounts. At December 31, 2019 the carrying value of inventory, included within prepayments and other current assets on the Consolidated Balance Sheet, was $3.2 million ( 2018 : $2.3 million ). (p) Property, plant and equipment Property, plant and equipment is stated at cost less accumulated depreciation. Depreciation of property, plant and equipment is computed using the straight line method based on the estimated useful lives of the assets as listed below: Years Building 40 Computer equipment and software 2-8 Office furniture and fixtures 8 Laboratory equipment 5 Motor vehicles 5 Leasehold improvements are amortized using the straight line method over the estimated useful life of the asset or the lease term, whichever is shorter. (q) Leases The Company adopted ASC 842 'Leases' ( ASC 842), with a date of initial application of January 1, 2019. The lease accounting policy applied in preparation of the results for the year ended December 31, 2019 therefore reflect application of ASC 842. ICON adopted the standard using the cumulative-effect adjustment approach. Under this transition method, ICON has applied the new standard as at the date of initial application (i.e. January 1, 2019), without restatement of comparative period amounts. The cumulative effect of applying the new standard is recorded as an adjustment to the opening consolidated balance sheet as at the date of initial application (see note 24 - Impact of new accounting pronouncements for further details). The comparative information has not been adjusted and therefore continues to be reported under ASC 840 'Leases' (ASC 840) . The new standard requires lessees to recognize the rights and obligations resulting from virtually all leases on the Consolidated Balance Sheet as right-of-use (ROU) assets with corresponding lease liabilities. The most significant impact of application of the new standard for ICON relates to the recognition of right-of-use assets and lease liabilities on the Consolidated Balance Sheet for operating leases for certain property, vehicles and equipment. Prior to application of ASC 842, costs in respect of operating leases were charged to the Consolidated Statements of Operations on a straight-line basis over the lease term. Pursuant to certain practical expedients available as part of adopting ASC 842, ICON has not reassessed; whether existing or expired contracts are or contain leases, the classification of existing or expired leases, or whether unamortized initial direct costs meet the new definition of initial direct costs under ASC 842. Additionally, ICON has elected to use hindsight in determining the lease term and in assessing impairment of ROU assets, if any. ICON determines if an arrangement is a lease at inception. Finance leases, if any, are depreciated on the same basis as property, plant and equipment. At December 31, 2019 and December 31, 2018 , the Group did not account for any leases as finance leases. Operating leases are included in operating right-of-use assets, other liabilities and non-current operating lease liabilities on our Consolidated Balance Sheet with the lease charge recognized on a straight-line basis over the lease term. ROU assets and lease liabilities are recognized based on the present value of future minimum lease payments over the lease term at commencement date or date of transition. Our lease terms may also include options to extend or terminate. ICON actively reviews options to extend or terminate leases and adjusts the ROU asset and lease liability when it is reasonably certain the option will be exercised. The ROU asset is adjusted for any prepayments made at the date of commencement and any initial direct costs incurred. As most of ICON's leases do not provide an implicit rate, the discount rate used is based on the rate of traded corporate bonds available at the commencement date adjusted for country risk, liquidity and lease term. Leasehold improvements are amortized over the shorter of the depreciable lives of the corresponding fixed assets or the lease term including any applicable renewals. Certain property leases include variable lease payments resulting from periodic rent increases based on an index which are recognized as incurred on the Consolidated Statements of Operations. ICON accounts for lease and non-lease components separately with lease components flowing through the Consolidated Balance Sheet and non-lease components expensed directly to the Consolidated Statements of Operations. In some cases, ICON enters into sublease agreements and becomes both a lessee and a lessor for the same underlying asset. Although subleases are accounted for separately from the lease they relate to, subleases are accounted for in the same way as other leases. The lease accounting policy applied in preparation of the results for the year ended December 31, 2018 reflected the application of ASC 840. Under this accounting policy, costs in respect of operating leases are charged to the Consolidated Statement of Operations on a straight line basis over the lease term. Assets acquired under capital finance leases are included in the Consolidated Balance Sheet at the present value of the future minimum lease payments and are depreciated over the shorter of the lease term and their remaining useful lives. The corresponding liabilities are recorded in the Consolidated Balance Sheet and the interest element of the capital lease rental is charged to interest expense. (r) Income taxes The Company applies the asset and liability method of accounting for income taxes. Under the asset and liability method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and for operating loss and tax credit carry-forwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which these temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. Deferred tax assets are reduced by a valuation allowance to the amount more likely than not to be realized. The Company recognizes the effect of income tax positions only if those positions will more likely than not be sustained. Recognized income tax positions are measured at the largest amount of tax benefit that is greater than 50 percent likely of being realized upon settlement. Interest and penalties related to income taxes are included in income tax expense and classified with the related liability on the Consolidated Balance Sheet. The Company accounts for the impact of GILTI (“global intangible low-taxed income”) as a period item in the period it arises and has therefore not provided for deferred taxes in respect of this item. (s) Government grants Government grants received relating to capital expenditures are shown as deferred income and credited to income on a basis consistent with the depreciation policy of the relevant assets. Grants relating to categories of operating expenditures are credited to income in the period in which the expenditure to which they relate is charged. Under the grant agreements amounts received may become repayable in full should certain circumstances specified within the grant agreements occur, including downsizing by the Company, disposing of the related assets, ceasing to carry on its business or the appointment of a receiver over any of its assets. The Company has not recognized any loss contingency having assessed as remote the likelihood of these events arising. (t) Research and development credits Research and development credits are available to the Company under the tax laws in certain jurisdictions, based on qualifying research and development spend as defined under those tax laws. Research and development credits are generally recognized as a reduction of income tax expense. However, certain tax jurisdictions provide refundable credits that are not wholly dependent on the Company's ongoing income tax status or income tax position. In these circumstances the benefit of these credits is not recorded as a reduction to income tax expense, but rather as a reduction of operating expenditure. (u) Pension costs The Company contributes to defined contribution plans covering all eligible employees. The Company contributes to these plans based upon various fixed percentages of employee compensation and such contributions are expensed as incurred. The Company operates, through two subsidiaries, a defined benefit plan for certain of its United Kingdom and Swiss employees. The Company accounts for the costs of these plans in accordance with ASC 715-30 'Defined Benefit Plans – Pension' . These plans are presented in accordance with the requirements of ASC 715-60 'Defined Benefit Plans – Other Postretirement' . (v) Net income per ordinary share Basic net income per ordinary share attributable to the Group has been computed by dividing net income available to ordinary shareholders by the weighted average number of ordinary shares outstanding during the period. Diluted net income per ordinary share is computed by adjusting the weighted ave

Investments

Investments	12 Months Ended
	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Investments	Investments (a) Available for sale investments December 31, 2019 December 31, 2018 (in thousands) Available for sale investments at start of year $59,910 $77,589 Purchases 9,603 80,956 Sales and maturities (21,686 ) (99,865 ) Interest on short term investments 1,065 1,329 Realized gain on sale of short term investments 55 56 Unrealized capital gain/(loss) – investments 681 (155 ) Available for sale investments at end of year $49,628 $59,910 The Company classifies its investment in short term investments as available for sale. Short term investments comprise highly liquid investments with maturities of greater than three months and minimum "A-" rated fixed and floating rate securities. Short term investments at December 31, 2019 have an average maturity of 0.65 years compared to 1.22 years at December 31, 2018 . The investments are reported at fair value with unrealized gains or losses reported in a separate component of shareholders' equity. Any differences between the cost and fair value of investments are represented by accrued interest and unrealized gains/losses. The fair value of short term investments are represented by level 1 fair value measurements – quoted prices in active markets for identical assets. The following table represents our available for sale short term investments by major security type as of December 31, 2019 : Maturity by period Cost Total Unrealized gains / (losses) Fair Value Total Less than 1 year 1 to 5 years (U.S.$ in millions) US government debt securities 14.91 0.16 15.07 6.01 9.06 Corporate securities 32.57 0.08 32.65 29.64 3.01 Term deposits 1.91 — 1.91 0.68 1.23 Total (U.S.$ in millions) $49.39 $0.24 $49.63 $36.33 $13.30 The contractual maturity of certain investments in the portfolio is greater than 12 months; however, classification as short-term investments reflects the Company practice and intention in respect of these investments. The Company recognizes the unrealized losses at fair value in equity as these unrealized losses on short term investments have been considered as temporary. (b) Investments in equity - long term The Company entered into subscription agreements with a number of funds. Capital totaling $10.1 million had been advanced under the terms of the subscription agreements at December 31, 2019 ( December 31, 2018 : $6.2 million ). The Company determined that the interests in the funds meet the definition of equity securities without readily determinable fair values. Effective from January 1, 2018, the Company concluded that the interests held at December 31, 2019 qualify for the NAV practical expedient in ASC 820 ' Fair value measurements and disclosure s'. There was a decrease in fair value of $0.8 million ( December 31, 2018 : increase in fair value of $0.8 million ) recognized in net income during the year bringing the carrying value of the subscriptions to $10.1 million at December 31, 2019 ( December 31, 2018 : $7.0 million ). The Company had committed to future investments of $22.5 million

Goodwill

Goodwill	12 Months Ended
	Dec. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	Goodwill December 31, 2019 December 31, 2018 (in thousands) Opening goodwill $ 756,260 $ 769,058 Current year acquisitions 126,932 — Prior period acquisition (note 4 (d)) — 1,048 Foreign exchange movement (22 ) (13,846 ) Closing goodwill $ 883,170 $ 756,260 The Company has made a number of strategic acquisitions since inception to enhance its capabilities and experience in certain areas of the clinical development process. Goodwill arising on acquisition represents the excess of the cost of acquired entities over the net amounts assigned to assets acquired and liabilities assumed. Goodwill primarily comprises of the acquired workforce in place which does not qualify for recognition as an asset apart from goodwill. The Company tests goodwill annually for impairment or whenever events occur which may indicate impairment. The results of the Company's goodwill impairment testing assessed at September 30, 2019 during the year ended December 31, 2019 provided no evidence of impairment and indicated the existence of sufficient headroom such that a reasonably possible change to the key assumptions used would be unlikely to result in an impairment of the related goodwill. Acquisitions (a) Symphony On September 24, 2019 a subsidiary of the Company, ICON Clinical Research LLC, acquired a 100% interest in Symphony. Symphony is a leading provider of at-home trial services and site support services. The acquisition of Symphony further enhances our site & patient services offering. The acquisition resulted in the recognition of goodwill of $23.1 million . The acquisition of Symphony has been accounted for as a business combination in accordance with ASC 805 ' Business Combinations' . The Company has made a provisional assessment of the fair value of assets acquired and liabilities assumed as at that date. September 24, 2019 (in thousands) Cash & cash equivalents $ 3,292 Property, plant and equipment 564 Operating right of use assets 820 Goodwill * 23,072 Customer relationships ** 7,975 Order backlog ** 2,140 Accounts receivable 3,579 Unbilled revenue 186 Prepayments and other current assets 181 Other receivables 6 Accounts payable (799 ) Unearned revenue (1,446 ) Other liabilities (933 ) Current lease liabilities (289 ) Non-current lease liabilities (531 ) Net assets acquired $ 37,817 Cash outflows $ 34,976 Contingent consideration payable 2,500 Working capital adjustment payable 341 Total consideration $ 37,817 *Goodwill represents the acquisition of an established workforce and the capability to provide at-home trial services and site support solutions. The full amount of the goodwill recognized is expected to be deductible for income tax purposes. **The Company has made an estimate of separate intangible assets acquired, being customer relationships and order book assets. The fair value of Symphony’s intangible assets has been measured provisionally, pending receipt of a final independent valuation. This assessment will be finalized within 12 months of the date of acquisition. The contingent consideration is based on revenue targets set for the Company to the period ending March 31, 2020. The fair value of the contingent consideration on acquisition was $2.5 million based on an income approach. The payment of contingent consideration will be in the range of zero to a maximum of $2.5 million . Due to the short term nature of the contingent consideration, no discounting has been applied. There has been no movement in the value of the contingent consideration from the date of acquisition to the year ended December 31, 2019. As the fair value measure is based on significant inputs that are not observable in the market, the contingent consideration meets the definition of a level 3 financial instrument under ASC 820. The inputs that are not observable in the market are the expected revenue of the Company to the period ending March 31, 2020 and the probability of achievement of this revenue target by the Company. A positive or negative movement of these inputs by 10% would not result in a material change to the contingent consideration balance at December 31, 2019. If new information obtained within one year of the date of acquisition about facts and circumstances that existed at the date of acquisition identifies adjustments to the above amounts, or any additional amounts that existed at the date of acquisition, then the accounting for the acquisition will be revised. Since September 24, 2019, Symphony has earned revenue of $4.5 million and net income of $1.0 million in the year ended December 31, 2019. The proforma effect of the Symphony acquisition if completed on January 1, 2018 would have resulted in revenue, net income and earnings per share for the fiscal years ending December 31, 2019 and December 31, 2018 as follows: Year Ended 2019 2018 (in thousands) Revenue $ 2,818,280 $ 2,609,233 Net income $ 376,636 $ 324,671 Basic earnings per share $ 6.90 $ 6.00 Diluted earnings per share $ 6.84 $ 5.93 b) MeDiNova On May 23, 2019 a subsidiary of the Company, ICON Clinical Research (U.K.) Limited acquired a 60% majority shareholding in MeDiNova, a site network with research sites in key markets in Europe and Africa. ICON has the right to acquire the remaining shares in the company during 2020. The vendors also have a right to sell the remaining shares to ICON during 2020. The acquisition further enhances ICON's patient recruitment capabilities in EMEA and complements ICON's existing site network in the US, PMG Research. The acquisition resulted in the recognition of goodwill of $81.4 million . The acquisition of MeDiNova has been accounted for as a business combination in accordance with ASC 805 ' Business Combinations' . The Company has made a provisional assessment of the fair value of assets acquired and liabilities assumed as at that date. May 23, 2019 (in thousands) Cash & cash equivalents $ 7,719 Property, plant and equipment 670 Operating right of use assets 1,558 Goodwill * 81,430 Customer relationships ** 3,887 Order backlog ** 171 Patient database ** 2,542 Accounts receivable 3,488 Unbilled revenue 4,272 Other receivables 819 Prepayments and other current assets 406 Accounts payable (5,484 ) Unearned revenue (5,796 ) Other liabilities (6,622 ) Current lease liabilities (430 ) Non-current lease liabilities (1,128 ) Non-current deferred tax liability (1,226 ) Net assets acquired $ 86,276 Cash outflows $ 54,123 Working capital adjustment receivable (439 ) Redeemable noncontrolling interest *** 32,592 Total consideration (including redeemable noncontrolling interest) $ 86,276 *Goodwill represents the acquisition of an established workforce and access to a broad site network in Europe and Africa. None of the goodwill recognized is expected to be deductible for income tax purposes. **The Company has made an estimate of separate intangible assets acquired, being customer relationships, order book assets and patient database. This assessment will be finalized within 12 months of the date of acquisition. The fair value of MeDiNova’s intangible assets has been measured provisionally, pending receipt of a final independent valuation. ***The fair value of the redeemable noncontrolling interest on May 23, 2019 was $32.6 million which was estimated by applying an income based approach. The valuation approach used was based on the future earnings of the Company times an appropriate earnings multiple. Redemption of the noncontrolling interest will be based on the Company's earnings to March 31, 2020. If new information obtained within one year of the date of acquisition about facts and circumstances that existed at the date of acquisition identifies adjustments to the above amounts, or any additional amounts that existed at the date of acquisition, then the accounting for the acquisition will be revised. Since May 23, 2019, MeDiNova has earned revenue of $6.5 million (after elimination of intercompany revenue from ICON) and net income of $4.7 million in the year ended December 31, 2019. The proforma effect of the MeDiNova acquisition if completed on January 1, 2018 would have resulted in revenue, net income and earnings per share for the fiscal years ending December 31, 2019 and December 31, 2018 as follows: Year Ended 2019 2018 (in thousands) Revenue $ 2,807,788 $ 2,599,091 Net income $ 375,979 $ 323,759 Basic earnings per share $ 6.89 $ 5.98 Diluted earnings per share $ 6.83 $ 5.91 (c) MMD On January 25, 2019 a subsidiary of the Company, ICON Laboratory Services Inc. acquired 100% of the share capital of MMD. MMD is a molecular diagnostic specialty laboratory that enables the development and commercialization of precision medicines in oncology. The acquisition resulted in the recognition of goodwill of $22.4 million . The acquisition of MMD has been accounted for as a business combination in accordance with ASC 805 ' Business Combinations' . The Company made an assessment of the fair value of assets acquired and liabilities assumed as at that date. The following table summarizes the Company’s fair values of the assets acquired and liabilities assumed: January, 25 2019 (in thousands) Cash & cash equivalent $ 686 Property, plant and equipment 1,697 Operating right of use assets 2,866 Goodwill * 22,430 Customer relationships * 10,708 Order backlog * 2,787 Accounts receivable 3,100 Unbilled revenue 2,421 Other receivables 43 Prepayments and other current assets 908 Deferred tax asset 1,568 Accounts payable (1,280 ) Unearned revenue (540 ) Other liabilities (1,232 ) Current lease liabilities (699 ) Non-current lease liabilities (2,167 ) Non-current other liabilities (1,123 ) Net assets acquired $ 42,173 Cash outflows $ 42,349 Working capital adjustment (176 ) Total consideration $ 42,173 *Goodwill represents the acquisition of an established workforce with experience in molecular diagnostic specialty laboratory services and commercialization of precision medicines in oncology. None of the goodwill recognized is expected to be deductible for income tax purposes. In finalizing the goodwill on acquisition of MMD in the twelve month period from acquisition, fair value adjustments were made which resulted in increases in unbilled revenue ( $2.1 million ), deferred tax asset ( $3.7 million ), accounts payable ( $0.6 million ) and other liabilities ( $0.1 million ) and decreases in property, plant and equipment ( $0.1 million ) and unearned revenue ( $0.9 million ). Customer relationship and order backlog assets were also finalized. Since January 25, 2019, MMD has earned revenue of $17.9 million and net income of $1.1 million in the year ended December 31, 2019. The proforma effect of the MMD acquisition if completed on January 1, 2018 would have resulted in revenue, net income and earnings per share for the fiscal years ending December 31, 2019 and December 31, 2018 as follows: Year Ended 2019 2018 (in thousands) Revenue $ 2,806,908 $ 2,612,346 Net income $ 373,930 $ 321,698 Basic earnings per share $ 6.85 $ 5.94 Diluted earnings per share $ 6.79 $ 5.87 (d) Mapi Group On July 27, 2017, a subsidiary of the Company, ICON Clinical Research Limited, acquired Mapi Group. Mapi Group is a leading patient-centered health outcomes research and commercialization company. Cash outflows on acquisition were $145.8 million . The acquisition agreement provided for working capital targets to be achieved. The acquisition resulted in the recognition of goodwill of $130.3 million . The acquisition of Mapi has been accounted for as a business combination in accordance with ASC 805 'Business Combinations' . The table following summarizes the Company’s assessment of the fair values of the assets acquired and liabilities assumed: July 27, 2017 (in thousands) Cash $ 19,649 Property, plant and equipment 4,872 Goodwill* 130,270 Order backlog 13,012 Customer relationships 18,392 Accounts receivable 15,874 Unbilled revenue 6,984 Prepayments and other current assets 2,587 Other receivables 1,430 Income taxes receivable 4,262 Accounts payable (2,994 ) Payments on account (31,445 ) Other liabilities (24,952 ) Non-current other liabilities (1,061 ) Non-current deferred tax liability (11,104 ) Net assets acquired $ 145,776 Cash outflows $ 144,131 Working capital adjustment 1,645 Total consideration $ 145,776 *Goodwill represents the acquisition of an established workforce with experience in late phase commercialization, analytics, real world evidence generation and strategic regulatory services in clinical trial services for biologics, drugs and devices. Goodwill related to the business acquired is not tax deductible. In finalizing the goodwill on acquisition of Mapi in the twelve month period from acquisition, fair value adjustments were made which resulted in increases in other liabilities ( $3.9 million ), plant and equipment ( $1.7 million ) and accounts receivable ( $1.7 million ) and income taxes receivable ( $1.5 million ) and decreases in unbilled revenue ( $4.8 million ), prepayments and other current assets ( $1.9 million ) and other receivables ( $1.0 million ) and in payment on account ( $2.6 million ) and non-current deferred tax liability ( $9.1 million ). Customer relationship and order backlog assets were also finalized. The proforma effect of the Mapi acquisition if completed on January 1, 2016 would have resulted in net revenue, net income and earnings per share for the fiscal years ending December 31, 2017 and December 31, 2016 as follows: Year Ended 2017 2016 (in thousands) Net revenue $ 1,811,018 $ 1,750,643 Net income $ 284,903 $ 263,101 Basic earnings per share $ 5.26 $ 4.76 Diluted earnings per share $ 5.19 $ 4.66

Intangible Assets

Intangible Assets	12 Months Ended
	Dec. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	Intangible Assets December 31, 2019 December 31, 2018 Cost (in thousands) Customer relationships $ 132,192 $ 109,622 Technology asset 11,169 11,169 Order backlog 36,318 31,220 Trade names/ brands 2,766 2,766 Volunteer list 1,325 1,325 Non-compete arrangements 489 489 Patient database 2,542 — Foreign exchange movement (5,728 ) (5,085 ) Total cost 181,073 151,506 Accumulated amortization (116,196 ) (100,249 ) Foreign exchange movement 3,017 2,798 Net book value $ 67,894 $ 54,055 On September 24, 2019 a subsidiary of the Company, ICON Clinical Research LLC, acquired a 100% interest in Symphony. Symphony is a leading provider of at-home trial services and site support services. The acquisition of Symphony further enhances our site & patient services offering. The value of certain customer relationships and order backlog identified of $8.0 million and $2.1 million respectively were recognized on acquisition and are being amortized over approximately 12 years and 2 years , the estimated period of benefit. In total, $0.5 million has been amortized in the period since the date of acquisition. On May 23, 2019 a subsidiary of the Company, ICON Clinical Research (U.K.) Limited acquired a majority shareholding in MeDiNova, a site network with research sites in key markets in Europe and Africa. ICON has the right to acquire the remaining shares in the company during 2020. The vendors also have a right to sell the remaining shares to ICON during 2020. The acquisition further enhances ICON's patient recruitment capabilities in EMEA and complements ICON's existing site network in the US, PMG Research. The value of certain customer relationships, patient database and order backlog identified of $3.9 million , $2.5 million and $0.2 million respectively were recognized on acquisition and are being amortized over approximately 12 years , 7 years and 1 year , the estimated period of benefit. In total, $0.5 million has been amortized in the period since the date of acquisition. On January 25, 2019 a subsidiary of the Company, ICON Laboratory Services Inc. acquired 100% of the share capital of MMD. MMD is a molecular diagnostic specialty laboratory that enables the development and commercialization of precision medicines in oncology. The value of certain customer relationships and order backlog identified of $10.7 million and $2.8 million respectively were recognized on acquisition and are being amortized over approximately over 16 years and 2 years , the estimated period of benefit. In total, $1.9 million has been amortized in the period since the date of acquisition. On July 27, 2017, a subsidiary of the Company, ICON Clinical Research Limited acquired Mapi Group. Mapi is a leading patient-centered health outcomes research and commercialization company. The acquisition of Mapi strengthens ICON’s existing commercialization and outcomes research business adding significant commercialization presence, analytics, real world evidence generation and strategic regulatory services. The value of certain customer relationships and order backlog identified of $18.4 million and $13.0 million respectively were recognized on acquisition and are being amortized over approximately over 8 years and 8.5 years , the estimated period of benefit. In total, $9.5 million has been amortized in the period since the date of acquisition. On September 15, 2016, a subsidiary of the Company, ICON US Holdings Inc., acquired ICON Government & Public Health Solutions (''GPHS'') (formerly Clinical Research Management (ClinicalRM)), a full-service CRO specializing in preclinical through Phase IV support of clinical research and clinical trial services for biologics, drugs and devices. The organization helps customers progress their products to market faster with a wide array of research, regulatory and sponsor services within the U.S. and around the globe. GPHS provides full service and functional research solutions to a broad range of US government agencies. The value of certain customer relationship, order backlog and brand assets identified of $4.0 million , $1.7 million and $1.4 million respectively are being amortized over approximately 7 years , 2 years and 5 years respectively, the estimated period of benefit. In total, $5.0 million has been amortized in the period since the date of acquisition. On December 4, 2015, a subsidiary of the Company, ICON Clinical Research LLC, acquired PMG, an integrated network of 52 clinical research sites in North Carolina, South Carolina, Tennessee, Illinois and Iowa. The site network includes wholly owned facilities and dedicated clinical research sites. PMG conducts clinical trials in all major therapeutic areas and has particular expertise in vaccine, gastroenterology, cardiovascular, neurology and endocrinology studies. The value of certain customer relationship and order backlog assets identified of $6.9 million and $3.0 million respectively are being amortized over approximately 7 years and 2 years respectively, the estimated period of benefit. In total, $7.0 million has been amortized in the period since the date of acquisition. The order backlog was fully amortized at December 31, 2019 . On February 27, 2015, a subsidiary of the Company, ICON Holdings Unlimited Company (formerly ICON Holdings), acquired MediMedia Pharma Solutions. Headquartered in Yardley, Pennsylvania, MediMedia Pharma Solutions includes MediMedia Managed Markets and Complete Healthcare Communications. MediMedia Managed Markets is a leading provider of strategic payer-validated market access solutions. Complete Healthcare Communications is one of the leading medical and scientific communication agencies working with medical affairs, commercial and brand development teams within life science companies. The value of certain customer relationships and order backlog identified of $22.8 million and $2.5 million respectively are being amortized over approximately 7 years and 1 year , the estimated period of benefit. $18.2 million has been amortized in the period since the date of acquisition. The order backlog is fully amortized at December 31, 2019 . On May 7, 2014, a subsidiary of the Company, ICON US Holdings Inc., acquired Aptiv Solutions, Inc. ("Aptiv"), a global biopharmaceutical and medical device development services company and leader in adaptive clinical trials. Aptiv offers full-service clinical trial consulting and regulatory support for drugs, medical devices and diagnostics with a specific focus on strategy to increase product development efficiency and productivity. The value of certain customer relationships and order backlog identified of $21.4 million and $7.9 million respectively are being amortized over approximately 7 years and 3 years , the estimated period of benefit. In total, $25.2 million has been amortized in the period since the date of acquisition. The order backlog is fully amortized at December 31, 2019 . On February 28, 2012, a subsidiary of the Company, ICON Clinical Research LLC (formerly ICON Clinical Research, Inc.), acquired PriceSpective, a strategy consulting company. The value of certain customer relationships identified of $10.2 million are being amortized over approximately 10 years , the estimated period of benefit. The value of order backlog and certain non-compete arrangements identified of $0.4 million and $0.4 million respectively were amortized over approximately 0.8 years and 3 years , the estimated period of benefit and were fully amortized at December 31, 2019 . In total, $8.8 million has been amortized in the period since the date of acquisition. On February 15, 2012, a subsidiary of the Company, ICON Clinical Research Limited, acquired BeijingWits Medical, a Chinese CRO. The value of certain customer relationships identified of $1.8 million are being amortized over approximately 10 years , the estimated period of benefit. The value of certain order backlog and non-compete arrangements identified of $0.4 million and $0.1 million respectively were amortized over approximately 4 years and 5 years , the estimated period of benefit and were fully amortized at December 31, 2019 . In total, $1.8 million has been amortized in the period since the date of acquisition. On July 14, 2011, a subsidiary of the Company, ICON Clinical Research Limited, acquired Firecrest Clinical Limited, a provider of technology solutions that boost investigator site performance and study management. The value of certain technology assets and customer relationships identified of $11.2 million and $5.2 million respectively are being amortized over approximately 7.5 years , the estimated period of benefit. The value of the Firecrest trade name and order backlog identified of $1.4 million and $1.2 million respectively were amortized over approximately 4.5 years and 1.2 years , the estimated period of benefit and were fully amortized at December 31, 2019 . In total, $16.5 million has been amortized in the period since the date of acquisition. Future intangible asset amortization expense for the years ended December 31, 2020 to December 31, 2024 is as follows: Year Ended December 31, 2019 (in thousands) 2020 $ 17,381 2021 13,711 2022 8,022 2023 6,176 2024 5,793 $ 51,083

Property, Plant and Equipment,

Property, Plant and Equipment, Net	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment, Net	Property, Plant and Equipment, net December 31, 2019 December 31, 2018 (in thousands) Cost Land $ 3,724 $ 3,476 Building 84,603 86,621 Computer equipment and software 434,445 399,192 Office furniture and fixtures 87,855 83,215 Laboratory equipment 40,495 36,092 Leasehold improvements 31,144 25,827 Motor vehicles 199 144 682,465 634,567 Less accumulated depreciation and asset write offs (517,378 ) (475,898 ) Property, plant and equipment (net) $ 165,087 $ 158,669

Other Liabilities

Other Liabilities	12 Months Ended
	Dec. 31, 2019
Other Liabilities Disclosure [Abstract]
Other Liabilities	Other Liabilities December 31, 2019 December 31, 2018 (in thousands) General trade and overhead liabilities* $ 174,131 $ 118,845 Personnel related liabilities 157,146 171,866 Operating lease liability (note 22) 28,320 — Facility related liabilities 11,138 14,012 Other liabilities 6,531 4,289 Restructuring and other items (note 14) 1,232 8,089 Short term government grants (note 11) 45 42 $ 378,543 $ 317,143 *includes amounts due to third parties in respect of accrued reimbursable expenses of $142.6 million at December 31, 2019 and $85.6 million

Non-Current Other Liabilities

Non-Current Other Liabilities	12 Months Ended
	Dec. 31, 2019
Payables and Accruals [Abstract]
Non-Current Other Liabilities	Non-Current Other Liabilities December 31, 2019 December 31, 2018 (in thousands) Other non-current liabilities $ 11,459 $ 10,126 Defined benefit pension obligations, net (note 9) 6,053 3,320 $ 17,512 $ 13,446

Employee Benefits

Employee Benefits	12 Months Ended
	Dec. 31, 2019
Retirement Benefits [Abstract]
Employee Benefits	Employee Benefits Certain Company employees are eligible to participate in a defined contribution plan (the "Plan"). Participants in the Plan may elect to defer a portion of their pre-tax earnings into a pension plan, which is run by an independent party. The Company matches participant's contributions typically at 8% of the participant's annual compensation. Contributions to the plan are recorded as an expense in the selling, general and administrative line in the Consolidated Statement of Operations. Contributions for the years ended December 31, 2019 , December 31, 2018 and December 31, 2017 were $26,483,000 , $25,241,000 and $20,355,000 respectively. The Company's United States operations maintain a retirement plan (the "U.S. Plan") that qualifies as a deferred salary arrangement under Section 401(k) of the Internal Revenue Code. Participants in the U.S. Plan may elect to defer a portion of their pre-tax earnings, up to the Internal Revenue Service annual contribution limit. The Company matches participant's contributions up to 3% and matches 50% of participant's contributions thereafter to a maximum Company contribution of 4.5% of the participant's annual compensation. Contributions to this U.S. Plan are recorded, in the year contributed, as an expense in the Consolidated Statement of Operations. Contributions for the years ended December 31, 2019 , December 31, 2018 and December 31, 2017 were $16,469,000 , $15,532,000 and $14,946,000 respectively. ICON Development Solutions Limited pension plan One of the Company's subsidiaries, ICON Development Solutions Limited, operates a defined benefit pension plan in the United Kingdom for its employees. The plan is managed externally and the related pension costs and liabilities are assessed in accordance with the advice of a professionally qualified actuary. Plan assets at December 31, 2019 , December 31, 2018 and December 31, 2017 , consist of units held in independently administered funds. The pension costs of this plan are presented in the following tables in accordance with the requirements of ASC 715-60 'Defined Benefit Plans – Other Postretirement' . The plan has been closed to new entrants with effect from July 1, 2003. Funded status December 31, 2019 December 31, 2018 (in thousands) Projected benefit obligation $ (37,036 ) $ (30,045 ) Fair value of plan assets 32,016 27,297 Funded status $ (5,020 ) $ (2,748 ) Non-current other liabilities (note 8) $ (5,020 ) $ (2,748 ) Change in benefit obligation December 31, 2019 December 31, 2018 (in thousands) Benefit obligation at beginning of year $ 30,045 $ 37,759 Service cost 107 124 Interest cost 867 895 Plan participants' contributions 24 24 Expenses — — Benefits paid (177 ) (3,049 ) Actuarial loss/(gain) 4,756 (3,844 ) Foreign currency exchange rate changes 1,414 (1,864 ) Benefit obligation at end of year $ 37,036 $ 30,045 Change in plan assets December 31, 2019 December 31, 2018 (in thousands) Fair value of plan assets at beginning of year $ 27,297 $ 32,423 Actual return/(loss) on plan assets 3,504 (584 ) Employer contributions 148 153 Plan participants' contributions 24 24 Benefits paid (177 ) (3,049 ) Foreign currency exchange rate changes 1,220 (1,670 ) Fair value of plan assets at end of year $ 32,016 $ 27,297 The fair values of the assets above do not include any of the Company's own financial instruments, property occupied by, or other assets used by, the Company. The following amounts were recorded in the Consolidated Statement of Operations as components of the net periodic benefit cost: December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Service cost $ 107 $ 124 $ 112 Interest cost 867 895 929 Expected return on plan assets (574 ) (624 ) (586 ) Amortization of net loss 67 248 250 Expenses — — (8 ) Net periodic benefit cost $ 467 $ 643 $ 697 The following assumptions were used at the commencement of the year in determining the net periodic pension benefit cost for the years ended December 31, 2019 , December 31, 2018 and December 31, 2017 : December 31, 2019 December 31, 2018 December 31, 2017 Discount rate 2.9 % 2.5 % 2.7 % Rate of compensation increase 3.7 % 3.7 % 3.9 % Expected rate of return on plan assets 2.1 % 2.0 % 2.1 % Other comprehensive income December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Actuarial loss/(gain) - benefit obligation $ 4,756 $ (3,844 ) $ 658 Actuarial (gain)/loss – plan assets (2,930 ) 1,208 (393 ) Actuarial loss recognized in net periodic benefit cost (67 ) (248 ) (250 ) Total $ 1,759 $ (2,884 ) $ 15 The estimated net loss and prior service cost for the defined benefit pension plan that will be amortized from accumulated other comprehensive income into net periodic benefit cost over the next year are $0.2 million and $Nil respectively. Amounts recognized in accumulated other comprehensive income that have not yet been recognized as components of net periodic benefit cost are as follows: December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Net actuarial loss $ 6,013 $ 4,254 $ 7,138 Total $ 6,013 $ 4,254 $ 7,138 Benefit Obligation The following assumptions were used in determining the benefit obligation at December 31, 2019 and December 31, 2018 : December 31, 2019 December 31, 2018 Discount rate 2.1 % 2.9 % Rate of compensation increase 3.3 % 3.7 % A single discount rate is used which, when used to discount the projected benefit cashflows underlying a pension scheme with a 26 year duration, gives the same result as a full AA corporate bond yield curve. Plan Assets The assets of the scheme are held on an investment platform with Mobius which invests in a number of investment funds with Legal & General, Stone Harbor, Investec and Barings. The overall investment strategy is that approximately 20% of investments are in world equities, corporate bonds, high yield bonds, multi-asset credit fund and senior secured loans, respectively. There is no self-investment in employer related assets. The expected long-term rate of return on assets at December 31, 2019 of 4.0% was calculated as the value of the fund after application of a market value reduction factor. The expected long term rates of return on different asset classes are as follows: Asset Category Expected long-term return per annum Corporate Bonds (including 50% high yield bonds) 3.4 % Equities 5.8 % Secured Loans and Multi Asset Credit 3.6 % Cash 2.1 % The long-term expected rate of return on cash is determined by reference to traditional corporate bond rates at the latest Balance Sheet date. The long-term expected returns on traditional corporate and government bonds are determined by reference to corporate bond yields and gilt yields respectively at the Balance Sheet date. The long-term expected returns on equities is based on the rate of return on government bonds with an allowance for out-performance. The long-term expected return on high yield bonds, secured loans and multi asset credit is based on the return on traditional corporate bonds with an allowance for out-performance. The underlying asset split of the fund is shown below. Asset Category December 31, 2019 December 31, 2018 Corporate Bonds (including 50% high yield bonds) 40 % 25 % Equities 21 % — % Secured Loans and Multi Asset Credit 39 % — % Gilts — % 71 % Cash — % 4 % 100 % 100 % Applying the above expected long term rates of return to the asset distribution at December 31, 2019 , gives rise to an expected overall rate of return of scheme assets of approximately 4.0% per annum. Plan Asset Fair Value Measurements Quoted Prices in Active Markets for Identical Assets Level 1 December 31, 2019 December 31, 2018 (in thousands) Cash $ 17 $ 1,029 Fixed Income Securities L&G Life GPBF All World Equity Index Fund 6,753 — L&G Life DC Active Corporate Bond 6,412 — Stone Harbor High Yield Bond Fund 6,292 — Investec Global Total Return Credit Fund 3,166 — Stone Harbor Multi Asset Credit Portfolio 3,151 — Barings European Loan Fund Buy & Hold 6,225 — Legal and General Active Corporate Bond – Over 10 Year — 6,688 Legal and General Gilt Funds — 7,136 Legal and General Index Linked Gilt Funds — 12,444 $ 32,016 $ 27,297 Cash Flows The Company expects to contribute $0.2 million to the pension fund in the year ending December 31, 2020 . The following annual benefit payments, which reflect expected future service as appropriate, are expected to be paid. (in thousands) 2020 $ 323 2021 398 2022 428 2023 419 2024 549 Years 2025 - 2029 $ 3,904 The expected cash flows are estimated figures based on the members expected to retire over the next 10 years assuming no early retirements, withdrawals or commutation of pension for cash. At the present time it is not clear whether annuities will be purchased when members reach retirement or whether pensions will be paid each month out of scheme assets. The cash flows above have been estimated on the assumption that pensions will be paid monthly out of scheme assets. If annuities are purchased, then the expected benefit payments will be significantly different from those shown above. Aptiv Solutions pension plan On May 7, 2014 the Company acquired 100% of the common stock of Aptiv Solutions ("Aptiv"). The acquisition of Aptiv was accounted for as a business combination in accordance with ASC 805 'Business Combinations' . The Company has a defined benefit plan covering its employees in Switzerland as mandated by the Swiss government. Benefits are based on the employee's years of service and compensation. Benefits are paid directly by the Company when they become due, in conformity with the funding requirements of applicable government regulations. The plan is managed externally and the related pension costs and liabilities are assessed in accordance with the advice of a professionally qualified actuary. Plan assets at December 31, 2019 and December 31, 2018 consist of units held in independently administered funds. The pension costs of this plan are presented in the following tables in accordance with the requirements of ASC 715-60 'Defined Benefit Plans – Other Postretirement' . Funded status December 31, 2019 December 31, 2018 (in thousands) Projected benefit obligation $ (7,047 ) $ (5,279 ) Fair value of plan assets 6,014 4,707 Funded status $ (1,033 ) $ (572 ) Non-current other liabilities (note 8) $ (1,033 ) $ (572 ) Change in benefit obligation December 31, 2019 December 31, 2018 (in thousands) Benefit obligation at beginning of year $ 5,279 $ 5,927 Service cost 115 138 Interest cost 40 47 Plan participants' contributions 67 83 Settlement — (409 ) Prior service cost — (8 ) Transferred (benefits paid)/balances (72 ) (77 ) Actuarial loss/(gain) 1,479 (372 ) Foreign currency exchange rate changes 139 (50 ) Benefit obligation at end of year $ 7,047 $ 5,279 Change in plan assets December 31, December 31, 2019 2018 (in thousands) Fair value of plan assets at beginning of year $ 4,707 $ 5,202 Expected return on plan assets 35 41 Actual return/(loss) on plan assets 1,114 (240 ) Scheme contributions 89 109 Plan participants' contributions 67 83 Transferred (benefits paid)/balances (72 ) (77 ) Settlement — (409 ) Foreign currency exchange rate changes 74 (2 ) Fair value of plan assets at end of year $ 6,014 $ 4,707 The fair values of the assets above do not include any of the Company's own financial instruments, property occupied by, or other assets used by, the Company. December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Service cost $ 115 $ 138 $ 243 Interest cost 40 47 54 Expected return on plan assets (35 ) (41 ) (47 ) Amortization of net gain (93 ) (69 ) (43 ) Amortization of prior service credit (9 ) (8 ) (8 ) Settlement — (93 ) (214 ) Net periodic benefit cost/(credit) $ 18 $ (26 ) $ (15 ) The following assumptions were used at the commencement of the year in determining the net periodic pension benefit cost for the years ended December 31, 2019 , December 31, 2018 and December 31, 2017 : December 31, 2019 December 31, 2018 December 31, 2017 Discount rate 0.80 % 0.80 % 0.75 % Rate of compensation increase 2.00 % 2.00 % 2.00 % Expected rate of return on plan assets 0.80 % 0.80 % 0.75 % Other comprehensive income December 31, 2019 December 31, 2018 December 31, 2017 Actuarial loss/(gain) - benefit obligation $ 1,479 $ (372 ) $ (626 ) Actuarial (gain)/loss – plan assets (1,114 ) 240 296 Prior service credit recognized in net periodic benefit cost — 93 215 Actuarial gain recognized in net periodic benefit cost 93 69 43 Amortization of net prior service credit 9 8 8 Net prior service cost occurring during the year — (9 ) (1 ) Total $ 467 $ 29 $ (65 ) The estimated net gain and prior service credit for the defined benefit pension plan that will be amortized from accumulated other comprehensive income into net periodic benefit cost over the next year are $6,000 and $9,000 respectively. Amounts recognized in accumulated other comprehensive income that have not yet been recognized as components of net periodic benefit cost are as follows: December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Net actuarial gain $ (787 ) $ (1,254 ) $ (1,283 ) Total $ (787 ) $ (1,254 ) $ (1,283 ) Benefit Obligation The following assumptions were used in determining the benefit obligation at December 31, 2019 and December 31, 2018 : December 31, 2019 December 31, 2018 Discount rate 0.30 % 0.80 % Rate of compensation increase 2.00 % 2.00 % The discount rate is determined by reference to Swiss corporate bond yields at the Balance Sheet date. Plan Assets The pension plan is an insured arrangement with Swiss Life. The assets are an insurance contract whose value depends on the amount saved by employees and the interest granted by Swiss Life. The value of assets does not depend on the performance of any underlying assets. There is no self-investment in employer related assets. Cash Flows The Company expects to contribute $0.1 million to its pension fund in the year ending December 31, 2020 . The following annual benefit payments, which reflect expected future service as appropriate, are expected to be paid. (in thousands) 2020 $ 280 2021 276 2022 270 2023 265 2024 259 Years 2025 - 2029 $ 1,184 The expected cash flows are estimated figures based on the members expected to retire over the next 10 years assuming no early retirements plus an additional amount based on recent average withdrawal experience. At the present time it is not clear whether annuities will be purchased when members reach retirement or whether pensions will be paid each month out of scheme assets. The cash flows above have been estimated on the assumption that pensions will be paid monthly out of scheme assets. If annuities are purchased, then the expected benefit payments will be significantly different from those shown above.

Equity Incentive Schemes and St

Equity Incentive Schemes and Stock Compensation Charges	12 Months Ended
	Dec. 31, 2019
Share-based Payment Arrangement [Abstract]
Equity Incentive Schemes and Stock Compensation Charges	Equity Incentive Schemes and Stock Compensation Charges Share Options On July 21, 2008 the Company adopted the Employee Share Option Plan 2008 (the "2008 Employee Plan") pursuant to which the Compensation and Organization Committee of the Company's Board of Directors may grant options to any employee, or any Director holding a salaried office or employment with the Company or a Subsidiary for the purchase of ordinary shares. On the same date, the Company also adopted the Consultants Share Option Plan 2008 (the "2008 Consultants Plan"), pursuant to which the Compensation and Organization Committee of the Company's Board of Directors may grant options to any consultant, adviser or non-executive Director retained by the Company or any Subsidiary for the purchase of ordinary shares. On February 14, 2017 both the 2008 Employee Plan and the 2008 Consultants Plan (together the "2008 Option Plans") were amended and restated in order to increase the number of options that can be issued under the 2008 Consultants Plan from 0.4 million to 1.0 million and to extend the date for options to be granted under the 2008 Option Plans. An aggregate of 6.0 million ordinary shares have been reserved under the 2008 Employee Plan, as reduced by any shares issued or to be issued pursuant to options granted under the 2008 Consultants Plan, under which a limit of 1.0 million shares applies. Further, the maximum number of ordinary shares with respect to which options may be granted under the 2008 Employee Option Plan, during any calendar year to any employee shall be 0.4 million ordinary shares. There is no individual limit under the 2008 Consultants Plan. No options may be granted under the 2008 Option Plans after February 14, 2027. Each option granted under the 2008 Option Plans will be an employee stock option, or NSO, as described in Section 422 or 423 of the Internal Revenue Code. Each grant of an option under the 2008 Options Plans will be evidenced by a Stock Option Agreement between the optionee and the Company. The exercise price will be specified in each Stock Option Agreement, however option prices will not be less than 100% of the fair market value of an ordinary share on the date the option is granted. On January 17, 2003 the Company adopted the Share Option Plan 2003 (the "2003 Share Option Plan") pursuant to which the Compensation and Organization Committee of the Board could grant options to officers and other employees of the Company or its subsidiaries for the purchase of ordinary shares. An aggregate of 6.0 million ordinary shares were reserved under the 2003 Share Option Plan; and in no event could the number of ordinary shares issued pursuant to options awarded under this plan exceed 10% of the outstanding shares, as defined in the 2003 Share Option Plan, at the time of the grant, unless the Board expressly determined otherwise. Further, the maximum number of ordinary shares with respect to which options could be granted under the 2003 Share Option Plan during any calendar year to any employee was 0.4 million ordinary shares. The 2003 Share Option Plan expired on January 17, 2013. No new options may be granted under this plan. Share option awards are granted with an exercise price equal to the market price of the Company's shares at date of grant. Prior to 2018, share options typically vest over a period of five years from date of grant and expire eight years from date of grant. Share options granted to non-executive directors during 2018 vest over 12 months and expire eight years from the date of grant. The following table summarizes the transactions for the Company's share option plans for the years ended December 31, 2019 , December 31, 2018 and December 31, 2017 : Options Granted Under Plans Weighted Average Exercise Price Weighted Average Grant Date Fair Value Outstanding at December 31, 2016 1,466,444 $ 43.45 $ 13.94 Granted 219,113 $ 85.98 $ 25.06 Exercised (458,243 ) $ 30.35 $ 10.72 Canceled (55,921 ) $ 54.35 $ 16.76 Outstanding at December 31, 2017 1,171,393 $ 56.02 $ 17.15 Granted 167,557 $ 118.90 $ 36.84 Exercised (408,699 ) $ 41.12 $ 13.55 Canceled (9,505 ) $ 32.35 $ 11.39 Outstanding at December 31, 2018 920,746 $ 74.32 $ 22.39 Granted 97,112 $ 140.13 $ 43.43 Exercised (329,870 ) $ 65.54 $ 19.78 Canceled/expired (31,881 ) $ 88.12 $ 26.77 Outstanding at December 31, 2019 656,107 $ 87.80 $ 26.60 Vested and exercisable at December 31, 2019 298,077 $ 68.72 $ 20.99 The weighted average remaining contractual life of options outstanding and options exercisable at December 31, 2019 , was 4.76 years and 3.64 years respectively ( 2018 : 5.01 years and 3.83 years respectively). 186,479 options are expected to vest during the year ended December 31, 2020 ( 241,149 options were expected to vest during the year ended December 31, 2019 ). The intrinsic value of options exercised during the year ended December 31, 2019 amounted to $26.2 million . The intrinsic value of options outstanding and options exercisable at December 31, 2019 amounted to $55.4 million and $30.9 million respectively. Intrinsic value is calculated based on the market value versus strike price of the Company's shares at the date of exercise. Non-vested shares outstanding as at December 31, 2019 are as follows: Options Outstanding Number of Shares Weighted Average Exercise Price Weighted Average Fair Value Non-vested outstanding at December 31, 2018 522,823 $ 88.18 $ 26.41 Granted 97,112 140.13 43.43 Vested (233,861 ) 84.91 25.68 Forfeited (28,044 ) 97.36 29.24 Non-vested outstanding at December 31, 2019 358,030 $ 103.68 $ 31.28 Outstanding and exercisable share options: The following table summarizes information concerning outstanding and exercisable share options as of December 31, 2019 : Options Outstanding Options Exercisable Range Exercise Price Number of Shares Weighted Average Remaining Contractual Life Weighted Average Exercise Price Number of Shares Weighted Average Exercise Price $ 22.30 35,405 0.32 35,405 $ 23.66 31 0.57 31 $ 26.71 450 0.69 450 $ 32.37 18,313 1.33 18,313 $ 36.22 645 1.46 645 $ 37.90 920 1.93 920 $ 40.83 22,740 2.39 22,740 $ 47.03 2,757 2.17 2,757 $ 48.67 10,128 2.21 10,128 $ 65.60 34,342 4.38 14,646 $ 66.47 3,445 3.39 2,096 $ 68.39 61,847 3.18 38,351 $ 71.95 100,123 4.17 68,595 $ 83.47 89,308 5.17 16,578 $ 90.03 52,082 5.38 23,594 $ 115.11 87,636 6.17 6,868 $ 125.74 41,270 6.38 35,960 $ 137.47 8,378 7.38 — $ 140.38 86,287 7.17 — — $22.30 - $140.38 656,107 4.76 $ 87.80 298,077 $ 68.72 Options outstanding include both vested and unvested options as at December 31, 2019 . Options exercisable represent options which have vested at December 31, 2019 . From the date of grant, substantially all options vest over a five year period at 20% per annum. Fair value of Stock Options Assumptions The weighted average fair value of options granted during the years ended December 31, 2019 , December 31, 2018 and December 31, 2017 was calculated using the Black-Scholes option pricing model. The weighted average fair values and assumptions were as follows: Year Ended December 31, 2019 December 31, 2018 December 31, 2017 Weighted average fair value $ 43.43 $ 36.84 $ 25.06 Assumptions: Expected volatility 30 % 30 % 29 % Dividend yield — % — % — % Risk-free interest rate 2.55 % 2.76 % 1.93 % Expected life 5.0 years 5.0 years 5.0 years Expected volatility is based on the historical volatility of our common stock over a period equal to the expected term of the options; the expected life represents the weighted average period of time that options granted are expected to be outstanding given consideration to vesting schedules and our historical experience of past vesting and termination patterns. The risk-free rate is based on the U.S. government zero-coupon bonds yield curve in effect at time of the grant for periods corresponding with the expected life of the option. Restricted Share Units and Performance Share Units On April 23, 2013 the Company adopted the 2013 Employees Restricted Share Unit and Performance Share Unit Plan (the "2013 RSU Plan") pursuant to which the Compensation and Organization Committee of the Company's Board of Directors may select any employee, or any Director holding a salaried office or employment with the Company, or a Subsidiary to receive an award under the plan. On May 11, 2015 the 2013 RSU Plan was amended and restated in order to increase the number of shares that can be issued under the RSU Plan by 2.5 million shares. Accordingly, an aggregate of 4.1 million ordinary shares have been reserved for issuance under the 2013 RSU Plan. The shares are awarded at par value and vest over a service period. Awards under the 2013 RSU Plan may be settled in cash or shares at the option of the Company. On April 30 2019, the Company approved the 2019 Consultants and Directors Restricted Share Unit Plan (the “2019 Consultants RSU Plan”), which was effective as of May 16, 2019, pursuant to which the Compensation and Organization Committee of the Company’s Board of Directors may select any consultant, adviser or non-executive Director retained by the Company, or a Subsidiary to receive an award under the plan. 250,000 ordinary shares have been reserved for issuance under the 2019 Consultants RSU Plan. The awards are at par value and vest over a service period. Awards granted to non-executive directors in May 2019 vest over twelve months . The Company has awarded RSUs and PSUs to certain key individuals of the Group. The following table summarizes RSU and PSU activity for the year ended December 31, 2019 : PSU Outstanding Number of Shares PSU Weighted Average Grant Date Fair Value PSU Weighted Average Remaining Contractual Life RSU Outstanding Number of Shares RSU Weighted Average Grant Date Fair Value RSU Weighted Average Remaining Contractual Life Outstanding at December 31, 2018 251,053 $ 85.95 0.96 534,677 $ 89.50 1.22 Granted 60,182 $ 140.13 160,237 $ 138.33 Shares vested (118,611 ) $ 71.45 (238,960 ) $ 69.19 Forfeited (16,635 ) $ 91.94 (66,054 ) $ 107.03 Outstanding at December 31, 2019 175,989 $ 110.79 1.04 389,900 $ 119.07 1.43 The fair value of RSUs vested for the year ended December 31, 2019 totaled $16.5 million ( 2018 : $18.8 million ). The fair value of PSUs vested for the year ended December 31, 2019 totaled $8.5 million ( 2018 : $14.7 million ). The PSUs vest based on service and specified EPS targets over the period 2017 – 2019, 2018 – 2020 and 2019 – 2021. Depending on the actual amount of EPS from 2017 to 2021 , up to an additional 75,615 PSUs may also be granted. Non-cash stock compensation expense Income from operations for the year ended December 31, 2019 is stated after charging $26.8 million in respect of non-cash stock compensation expense. Non-cash stock compensation expense has been allocated as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Direct costs $ 14,777 $ 17,408 $ 18,020 Selling, general and administrative 12,042 14,186 12,553 Total compensation costs $ 26,819 $ 31,594 $ 30,573 Total non-cash stock compensation expense not yet recognized at December 31, 2019 amounted to $42.4 million . The weighted average period over which this is expected to be recognized is 2.18 years . The income tax expense for the year ended December 31, 2019 reflects a net income tax benefit of $8.2 million in connection with stock compensation (including excess tax benefits) and the total tax benefit in connection with stock options exercised during 2019 was $1.9 million . The income tax expense for the year ended December 31, 2018 reflects a net income tax benefit of $12.7 million in connection with stock compensation (including excess tax benefits) and the total tax benefit in connection with stock options exercised during 2018 was $3.6 million . The income tax expense for the year ended December 31, 2017 reflects a net income tax benefit of $9.3 million in connection with stock compensation (excluding excess tax benefits) and the total tax benefit realized in connection with stock options exercised during 2017 was $3.2 million .

Government Grants

Government Grants	12 Months Ended
	Dec. 31, 2019
Deferred Revenue Disclosure [Abstract]
Government Grants	Government Grants December 31, 2019 December 31, 2018 (in thousands) Received $ 3,539 $ 3,539 Less accumulated amortization (2,836 ) (2,792 ) Foreign exchange translation adjustment 155 172 Total government grants 858 919 Less current portion (45 ) (42 ) Non-current government grants $ 813 $ 877 Capital grants received may be refundable in full if certain events occur. Such events, as set out in the related grant agreements, include sale of the related asset, liquidation of the Company or failure to comply with other conditions of the grant agreements. No loss contingency has been recognized as the likelihood of such events arising has been assessed as remote. Government grants amortized to the profit and loss account amounted to $44,000 for the year ended December 31, 2019 ( December 31, 2018 : $47,000 ). As at December 31, 2019 the Company had $3.1 million ( December 31, 2018 : $3.2 million ) in restricted retained earnings, pursuant to the terms of grant agreements.

Share Capital

Share Capital	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Share Capital	Share Capital Holders of ordinary shares will be entitled to receive such dividends as may be recommended by the Board of Directors of the Company and approved by the shareholders and/or such interim dividends as the Board of Directors of the Company may decide. On liquidation or a winding up of the Company, the par value of the ordinary shares will be repaid out of the assets available for distribution among the holders of the ordinary shares of the Company. Holders of ordinary shares have no conversion or redemption rights. On a show of hands, every holder of an ordinary share present in person or proxy at a general meeting of shareholders shall have one vote, for each ordinary share held with no individual having more than one vote. During the year ended December 31, 2019 , 329,870 options were exercised by employees at an average exercise price of $65.54 per share for total proceeds of $21.6 million . During the year ended December 31, 2019 , 237,119 ordinary shares were issued in respect of certain RSUs and 118,611 ordinary shares were issued in respect of PSUs previously awarded by the Company. During the year ended December 31, 2018 , 408,699 options were exercised by employees at an average exercise price of $41.12 per share for total proceeds of $16.8 million . During the year ended December 31, 2018 , 273,742 ordinary shares were issued in respect of certain RSUs and 215,826 ordinary shares were issued in respect of PSUs previously awarded by the Company. During the year ended December 31, 2017 , 458,243 options were exercised by employees at an average exercise price of $30.35 per share for total proceeds of $13.9 million . During the year ended December 31, 2017 , 361,102 ordinary shares were issued in respect of certain RSUs and 320,640 ordinary shares were issued in respect of PSUs previously awarded by the Company. (a) Share Repurchase Program On July 31, 2015 the Company commenced a buyback program of up to $400 million under which the Company could acquire its outstanding ordinary shares (by way of redemption), in accordance with Irish law, the United States securities laws and the Company's constitutional documents through open market share acquisitions. A total of 5,316,062 ordinary shares were redeemed by the Company under this buyback program for a total consideration of $400 million . The share buyback program was completed in December 31, 2015, with a total of 6,198,481 ordinary shares redeemed during the year ended December 31, 2015 for total consideration of $457.9 million (including the program for $400 million ). A resolution was passed at the Company’s Annual General Meeting (“AGM”) on July 22, 2016, which authorized the Directors to purchase (buyback) up to 10% of the outstanding shares in the Company. This authorization was renewed at the Company's AGM on each of July 25, 2017, July 24, 2018 and July 23, 2019. On October 3, 2016, the Company commenced a share buyback program of up to $400 million . The share buyback program was completed during the year ended December 31, 2018 with a total of 4,026,576 ordinary shares redeemed for a total consideration of $372.1 million . On January 8, 2019, the Company commenced a further share buyback program of up to 1.0 million ordinary shares which was completed during the year ended December 31, 2019 . These shares were redeemed by the Company for a total consideration of $141.6 million . On October 22, 2019, the Company commenced a further share buyback program. At December 31, 2019 , 35,100 ordinary shares were redeemed by the Company for a total consideration of $ 5.3 million . All ordinary shares that were redeemed under the buyback program were canceled in accordance with the Constitution of the Company and the nominal value of these shares transferred to other undenominated capital as required under Irish Company law. Under the repurchase program, a broker purchased the Company's shares from time to time on the open market or in privately negotiated transactions in accordance with agreed terms and limitations. The program was designed to allow share repurchases during periods when the Company would ordinarily not be permitted to do so because it may be in possession of material non-public or price-sensitive information or due to applicable insider trading laws or self-imposed trading blackout periods. The Company's instructions to the broker were irrevocable and the trading decisions in respect of the repurchase program were made independently of and uninfluenced by the Company. The Company confirms that on entering the share repurchase plans it had no material non-public, price-sensitive or inside information regarding the Company or its securities. Furthermore, the Company will not enter into additional plans whilst in possession of such information. The timing and actual number of shares acquired by way of the redemption will be dependent on market conditions, legal and regulatory requirements and the other terms and limitations contained in the program. In addition, acquisitions under the program may be suspended or discontinued in certain circumstances in accordance with the agreed terms. Therefore, there can be no assurance as to the timing or number of shares that may be acquired under the program.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company's United States and Irish based subsidiaries file income tax returns in the United States and Ireland respectively. Other foreign subsidiaries are taxed separately under the laws of their respective countries. The components of income before income tax expense are as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Ireland $ 323,726 $ 243,988 $ 218,306 United States 21,073 27,499 28,426 Other 82,190 93,127 81,325 Income before income tax expense $ 426,989 $ 364,614 $ 328,057 The components of income tax expense are as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Income tax expense: Current tax expense: Ireland $ 35,955 $ 28,042 $ 20,084 United States 5,073 2,885 5,792 Other 11,642 9,379 9,964 Total current tax expense 52,670 40,306 35,840 Deferred tax (benefit)/expense: Ireland 2,833 1,054 261 United States (3,502 ) 875 8,980 Other (868 ) (277 ) 1,488 Total deferred tax (benefit)/expense (1,537 ) 1,652 10,729 Income tax expense allocated to continuing operations 51,133 41,958 46,569 Impact on other comprehensive income of the income tax consequence of : Currency impact on long term funding 25 119 973 Fair value of cash flow hedge — (148 ) 148 Total $ 51,158 $ 41,929 $ 47,690 Ireland's statutory income tax rate is 12.5% . The Company's consolidated reported income tax expense differed from the amount that would result from applying the Irish statutory rate as set forth below: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Taxes at Irish statutory rate of 12.5% (2018:12.5%; 2017:12.5%) $ 53,374 $ 45,577 $ 41,007 Foreign and other income taxed at higher rates 7,356 7,649 6,324 Research & development tax incentives (893 ) (1,243 ) (830 ) Movement in valuation allowance (10 ) 5,667 1,329 Effects of change in tax rates 359 (147 ) 925 (Decrease)/increase in unrecognized tax benefits (1,273 ) (5,423 ) 933 Impact of stock compensation (7,383 ) (8,301 ) (9,917 ) Impact of deemed repatriation under US Tax Reform — — 7,694 Other (397 ) (1,821 ) (896 ) Provision for income taxes $ 51,133 $ 41,958 $ 46,569 In 2017, income tax expense included non-recurring items related to US Tax Reform (H.R.1). The income tax expense recognized in respect of deemed repatriation of historic earnings of non-U.S. subsidiaries owned by our U.S. subsidiaries was $7.7 million . The income tax expense recognized in respect of the change in the US federal income tax rate from 35% to 21% was $0.5 million (included in “Effects of change in tax rates” above). The tax effects of temporary differences that give rise to significant portions of deferred tax assets and deferred tax liabilities are presented below: December 31, 2019 December 31, 2018 (in thousands) Deferred tax liabilities: Property, plant and equipment $ 1,102 $ 981 Right-of-use-asset 11,838 — Goodwill 27,590 25,149 Intangible assets 11,805 9,397 Other 6,284 5,703 Total deferred tax liabilities recognized 58,619 41,230 Deferred tax assets: Operating loss and tax credits carryforwards 37,865 29,995 Property, plant and equipment 5,257 4,893 Lease Liabilities 11,754 — Accrued expenses and payments on account 26,380 24,599 Stock compensation 5,009 6,490 Deferred compensation 2,744 2,197 Unearned revenue 3,933 5,681 Other 604 2 Total deferred tax assets 93,546 73,857 Valuation allowance for deferred tax assets (27,721 ) (27,263 ) Deferred tax assets recognized 65,825 46,594 Overall net deferred tax asset $ 7,206 $ 5,364 At December 31, 2019 the Company has recognized a deferred tax asset of $11.8 million and a deferred tax liability of $11.8 million in respect of operating lease arrangements under which future tax deductions are attributable to the lease liability. At December 31, 2019 Ireland subsidiaries had tax credit carryforwards for income tax purposes that may be carried forward indefinitely, available for offset against future tax liabilities, if any, of $6.5 million . At December 31, 2019 U.S. subsidiaries had U.S. federal and state net operating loss ("NOL") carryforwards of approximately $22.2 million and $45.0 million , respectively. These NOLs are available for offset against future taxable income and the expiry dates are shown in the table below. Of the $22.2 million U.S. federal NOLs, approximately $7.0 million is available for offset against future U.S. federal taxable income in 2020. The subsidiary's ability to use the remaining U.S. federal and state NOL carryforwards is limited on an annual basis due to change of ownership in 2014, 2017, and 2019, as defined by Section 382 of the Internal Revenue Code of 1986, as amended. Of the U.S. federal NOLs, $20.2 million are limited by Section 382. Of the $20.2 million of losses, the amounts are available as follows: $10.0 million for the years 2020 - 2021, $9.8 million in 2022-2026, $0.4 million for the years 2027 – 2036. As at December 31, 2019 , U.S subsidiaries also had disallowed interest carryforwards of $29.3 million that can be carried forward indefinitely. These carryforwards are available for offset against future taxable income in the event that the U.S subsidiaries have excess capacity for interest deductions in future years. At December 31, 2019 other than those in the U.S. and Ireland, we had operating loss carryforwards for income tax purposes that may be carried forward indefinitely, available to offset against future taxable income, if any, of approximately $40.1 million . In addition at December 31, 2019 those subsidiaries had tax credit carryforwards for income tax purposes that may be carried forward indefinitely, available to offset against future tax liabilities, if any, of $5.1 million . At December 31, 2019 those subsidiaries also had additional operating loss carryforwards of $16.2 million which are due to expire between 2020 and 2026 and operating loss carryforwards of $19.1 million which are due to expire between 2027 and 2036. The expected expiry dates of these US losses are as follows: Federal NOL's State NOL's (in thousands) 2022-2035 $ 18,866 $ 44,986 2037 1,921 — Indefinite 1,363 49 $ 22,150 $ 45,035 In addition, US subsidiaries have alternative minimum tax credit carryforwards of approximately $0.3 million that are available to reduce future U.S. federal regular income taxes through 2020. Any remaining alternative minimum tax credits will be fully refundable in 2021. We also have general business tax credit carryforwards of approximately $1.0 million that are available to offset future U.S. federal and state income taxes. The general business tax credits are non-refundable and are due to expire between the years 2026-2038. The valuation allowance at December 31, 2019 was approximately $27.7 million . The valuation allowance for deferred tax assets as of December 31, 2018 and December 31, 2017 was $27.3 million and $22.4 million respectively. The net change in the total valuation allowance was an increase of $0.4 million during 2019 and an increase of $4.8 million during 2018 . Of the total increase of $0.4 million in 2019 , $ Nil resulted in current year income tax benefit and $0.4 million was recognized in Other Comprehensive Income. Of the total increase of $4.8 million in 2018 , $5.6 million resulted in a current year income tax expense, and $0.8 million was recognized in Other Comprehensive Income. The valuation allowances at December 31, 2019 and December 31, 2018 were primarily related to operating losses and tax credits carried forward that, in the judgment of management, are not more likely than not to be realized. In assessing the realizability of deferred tax assets, management considers whether it is more likely than not that some portion or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the periods in which those temporary differences become deductible. Management considers the scheduled reversal of deferred tax liabilities and projected future taxable income in making this assessment. In respect of deferred tax assets not subject to a valuation allowance, management considers that it is more likely than not that these deferred tax assets will be realized on the basis that there will be sufficient reversals of deferred tax liabilities and taxable income in future periods. During 2018 , the Company recognized a valuation allowance of $6.2 million in respect of disallowed interest carryforwards generated during the year as management does not consider it more likely than not that the Company will have sufficient capacity with which to utilize these losses. During 2019 , $3.4 million of this valuation allowance was released following a refinancing of the group's US subsidiaries. The Company has recognized a deferred tax liability of $5.4 million ( 2018 : $4.9 million ) for investments in foreign subsidiaries where the Company does not consider the earnings to be indefinitely reinvested. For the deferred tax liability not recognized in respect of temporary differences related to investments in foreign subsidiaries which are considered to be indefinitely reinvested, it is not practicable to calculate the exact unrecognized deferred tax liability, however it is not expected to be material as Ireland allows a tax credit in respect of distributions from foreign subsidiaries at the statutory tax rate in the jurisdiction of the subsidiary so that no material tax liability would be expected to arise in Ireland in the event these earnings were ever remitted. In addition, withholding taxes applicable to remittances from foreign subsidiaries would not be expected to be material given Ireland’s tax treaty network and the EU parent subsidiary directive. A reconciliation of the beginning and ending amount of total unrecognized tax benefits is as follows: December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Unrecognized tax benefits at start of year $ 21,433 $ 23,720 $ 26,620 Increase related to prior year tax positions — 2,084 — Decrease related to prior year tax positions — (2,915 ) (3,050 ) Increase related to current year tax positions 1,588 3,065 4,765 Settlements (347 ) (182 ) (2,523 ) Lapse of statute of limitations (2,518 ) (4,339 ) (2,092 ) Unrecognized tax benefits at end of year $ 20,156 $ 21,433 $ 23,720 The relevant statute of limitations for unrecognized tax benefits totaling $3.8 million could potentially expire during 2020. Included in the balance of total unrecognized tax benefits at December 31, 2019 were potential benefits of $20.2 million , which if recognized, would affect the effective rate on income tax from continuing operations. The balance of total unrecognized tax benefits at December 31, 2018 and December 31, 2017 included potential benefits which, if recognized, would affect the effective rate of income tax from continuing operations of $21.4 million and $23.7 million respectively. Interest and penalties recognized during the year ended December 31, 2019 amounted to $ Nil ( 2018 : net expense of $1.3 million , 2017 : net expense of $0.9 million ) and are included within the income tax expense. Total accrued interest and penalties as of December 31, 2019 and December 31, 2018 were $1.1 million and $1.1 million respectively and are included in closing income taxes payable at those dates. Our major tax jurisdictions are the United States and Ireland. We may potentially be subjected to tax audits in both our major jurisdictions. In the United States, tax periods open to audit include the years ended December 31, 2016 , December 31, 2017 , December 31, 2018 and December 31, 2019 . In Ireland, tax periods open to audit include the years ended December 31, 2015 , December 31, 2016 , December 31, 2017 , December 31, 2018 and December 31, 2019 . During such audits, local tax authorities may challenge the positions taken by us in our tax returns.

Restructuring Charges

Restructuring Charges	12 Months Ended
	Dec. 31, 2019
Restructuring and Related Activities [Abstract]
Restructuring Charges	Restructuring charges No restructuring charge was recognized during the year ended December 31, 2019 . Year Ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Restructuring charges $ — $ 12,490 $ 7,753 Net charge $ — $ 12,490 $ 7,753 Prior Period Restructuring Charges A restructuring charge of $12.5 million was recognized during the year ended December 31, 2018 , under a restructuring plan adopted following a review of operations. The restructuring plan reflected resource rationalization across the business to improve resource utilizations, resulting in a charge of $9.7 million and office consolidation resulting in the recognition of an onerous lease obligation of $2.8 million . No additional charge was recorded during the twelve months ended December 31, 2019 . Workforce reductions Onerous Lease Total (in thousands) Total provision recognized $ 9,684 $ 2,806 $ 12,490 Utilized (5,399 ) (672 ) $ (6,071 ) Provision at December 31, 2018 $ 4,285 $ 2,134 $ 6,419 Utilized (3,554 ) (1,228 ) (4,782 ) Provision at December 31, 2019 $ 731 $ 906 $ 1,637 A restructuring charge of $7.8 million was recognized during the year ended December 31, 2017 , under a restructuring plan adopted following a review of operations. The restructuring plan reflected resource rationalization across the business to improve resource utilization. No additional charge was recorded during the twelve months ended December 31, 2019 . Workforce (in thousands) Restructuring charges $ 7,753 Utilized (4,656 ) Provision at December 31, 2017 $ 3,097 Utilized (1,015 ) Provision at December 31, 2018 $ 2,082 Utilized (2,082 ) Provision at December 31, 2019 $ — At December 31, 2019 $1.2 million is included within other liabilities and $0.4 million within non-current other liabilities.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Litigation The Company is not party to any litigation or other legal proceedings that the Company believes could reasonably be expected to have a material adverse effect on the Company's business, results of operations and financial condition. Operating Leases The Company has several non-cancelable operating leases, primarily for facilities, that expire over the next twelve years . These leases generally contain renewal options and require the Company to pay all executory costs such as maintenance and insurance. The Company transitioned to ASC 842 'Leases' (ASC 842) with effect from January 1, 2019 under the cumulative effect adjustment approach (see note 28 - Impact of changes in accounting policies ). Under this transition method, ASC 842 is applied from January 1, 2019 without restatement of comparative period amounts. Results for the year ended December 31, 2018 and December 31, 2017 are therefore presented under the previous leasing accounting principles, ASC 840 ' Leases ' (ASC 840). Pursuant to ASC 840, the Company recognized $40.3 million and $44.0 million in rental expense, including rates, for the years ended December 31, 2018 and December 31, 2017 respectively. Future minimum rental commitments for operating leases with non-cancelable terms in excess of one year as of December 31, 2018 were as follows: Minimum rental payments (in thousands) 2019 32,634 2020 26,839 2021 21,306 2022 15,781 2023 10,829 Thereafter 19,194 Total 126,583 See note 22 - Operating leases for rental expense and future minimum rental commitments pursuant to ASC 842 for the year ended and as of December 31, 2019 .

Disaggregation of Revenue

Disaggregation of Revenue	12 Months Ended
	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	Disaggregation of Revenue Revenue disaggregated by customer profile is as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Top client $ 350,287 $ 352,335 $ 503,875 Clients 2-5 704,963 671,723 505,818 Clients 6-10 347,832 385,741 348,841 Clients 11-25 529,713 461,351 421,759 Other 873,044 724,627 622,028 Total $2,805,839 $2,595,777 $2,402,321 Revenue for the years ended December 31, 2019 and December 31, 2018 reflect revenue under ASC 606. Revenue for the year ended December 31, 2017 reflects gross revenue (including reimbursable costs) under ASC 605. Accounts receivable and unbilled revenue are as follows: December 31, 2019 December 31, 2018 (in thousands) Billed services (accounts receivable) $ 535,088 $ 423,680 Unbilled services (unbilled revenue) 422,769 362,926 Accounts receivable and unbilled revenue 957,857 786,606 Allowance for doubtful accounts (note 18) (7,380 ) (8,889 ) Accounts receivable and unbilled revenue, net $ 950,477 $ 777,717 Unbilled services and unearned revenue or payments on account (contract assets and liabilities) were as follows: (in thousands, except percentages) December 31, 2019 December 31, 2018 $ Change % Change Unbilled services (unbilled revenue) $ 422,769 $ 362,926 $ 59,843 16.5 % Unearned revenue (payments on account) (366,988 ) (274,468 ) (92,520 ) 33.7 % Net balance $ 55,781 $ 88,458 $ (32,677 ) 36.9 % Timing may differ between the satisfaction of performance obligations and the invoicing and collection of amounts related to our contracts with customers. We record assets for amounts related to performance obligations that are satisfied but not yet billed and/or collected. These assets are recorded as unbilled revenue and therefore contract assets rather than accounts receivables when receipt of the consideration is conditional on something other than the passage of time. Liabilities are recorded for amounts that are collected in advance of the satisfaction of performance obligations or billed in advance of the revenue being earned. Unbilled services/revenue balances arise where invoicing or billing is based on the timing of agreed milestones related to service contracts for clinical research. Contractual billing arrangements in respect of certain reimbursable expenses (principally investigators) require billing by the investigator to the Company prior to billing by the Company to the customer. As there is no contractual right of set-off between unbilled services (contract assets) and unearned revenue (contract liabilities), each are separately presented gross on the Consolidated Balance Sheet. The most significant impact of application of ASC 606 was the measurement of a clinical trial service as a single performance obligation recognized over time. We concluded that ICON is the contract principal in respect of both direct services and in the use of third parties (principally investigator services) that support a clinical trial. The progress towards completion for clinical service contracts is measured based on total project costs (including reimbursable costs). Reimbursable expenses are included within direct costs on adoption of ASC 606 and are recorded based on activity undertaken by the third party. Amounts owed to investigators and others in respect of reimbursable expenses at December 31, 2019 and December 31, 2018 were $142.6 million and $85.6 million (see note 7 - Other liabilities ). Unbilled services as at December 31, 2019 increased by $59.8 million as compared to December 31, 2018 . Unearned revenue increased by $92.5 million over the same period resulting in a decrease of $32.7 million in the net balance of unbilled services and unearned revenue or payments on account between December 31, 2018 and December 31, 2019 . These fluctuations are primarily due to timing of payments and invoicing related to the Group's clinical trial management contracts. Billings and payments are established by contractual provisions including predetermined payment schedules which may or may not correspond to the timing of the transfer of control of the Company's services under the contract. Unbilled services arise from long-term contract when a cost-based input method of revenue recognition is applied and revenue recognized exceeds the amount billed to the customer. The bad debt expense recognized on the Group's receivables and unbilled services was $0.4 million for the twelve months ended December 31, 2019 . As of December 31, 2019 approximately $5.3 billion of revenue is expected to be recognized in the future in respect of unsatisfied performance obligations. The Company expects to recognize revenue on approximately 48% of the unrealized performance obligation over the next twelve months

Accounts Receivable, Unbilled R

Accounts Receivable, Unbilled Revenue (Contract Assets) and Unearned Revenue Or Payments On Account (Contract Liabilities)	12 Months Ended
	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Accounts Receivable, Unbilled Revenue (Contract Assets) and Unearned Revenue Or Payments On Account	Disaggregation of Revenue Revenue disaggregated by customer profile is as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Top client $ 350,287 $ 352,335 $ 503,875 Clients 2-5 704,963 671,723 505,818 Clients 6-10 347,832 385,741 348,841 Clients 11-25 529,713 461,351 421,759 Other 873,044 724,627 622,028 Total $2,805,839 $2,595,777 $2,402,321 Revenue for the years ended December 31, 2019 and December 31, 2018 reflect revenue under ASC 606. Revenue for the year ended December 31, 2017 reflects gross revenue (including reimbursable costs) under ASC 605. Accounts receivable and unbilled revenue are as follows: December 31, 2019 December 31, 2018 (in thousands) Billed services (accounts receivable) $ 535,088 $ 423,680 Unbilled services (unbilled revenue) 422,769 362,926 Accounts receivable and unbilled revenue 957,857 786,606 Allowance for doubtful accounts (note 18) (7,380 ) (8,889 ) Accounts receivable and unbilled revenue, net $ 950,477 $ 777,717 Unbilled services and unearned revenue or payments on account (contract assets and liabilities) were as follows: (in thousands, except percentages) December 31, 2019 December 31, 2018 $ Change % Change Unbilled services (unbilled revenue) $ 422,769 $ 362,926 $ 59,843 16.5 % Unearned revenue (payments on account) (366,988 ) (274,468 ) (92,520 ) 33.7 % Net balance $ 55,781 $ 88,458 $ (32,677 ) 36.9 % Timing may differ between the satisfaction of performance obligations and the invoicing and collection of amounts related to our contracts with customers. We record assets for amounts related to performance obligations that are satisfied but not yet billed and/or collected. These assets are recorded as unbilled revenue and therefore contract assets rather than accounts receivables when receipt of the consideration is conditional on something other than the passage of time. Liabilities are recorded for amounts that are collected in advance of the satisfaction of performance obligations or billed in advance of the revenue being earned. Unbilled services/revenue balances arise where invoicing or billing is based on the timing of agreed milestones related to service contracts for clinical research. Contractual billing arrangements in respect of certain reimbursable expenses (principally investigators) require billing by the investigator to the Company prior to billing by the Company to the customer. As there is no contractual right of set-off between unbilled services (contract assets) and unearned revenue (contract liabilities), each are separately presented gross on the Consolidated Balance Sheet. The most significant impact of application of ASC 606 was the measurement of a clinical trial service as a single performance obligation recognized over time. We concluded that ICON is the contract principal in respect of both direct services and in the use of third parties (principally investigator services) that support a clinical trial. The progress towards completion for clinical service contracts is measured based on total project costs (including reimbursable costs). Reimbursable expenses are included within direct costs on adoption of ASC 606 and are recorded based on activity undertaken by the third party. Amounts owed to investigators and others in respect of reimbursable expenses at December 31, 2019 and December 31, 2018 were $142.6 million and $85.6 million (see note 7 - Other liabilities ). Unbilled services as at December 31, 2019 increased by $59.8 million as compared to December 31, 2018 . Unearned revenue increased by $92.5 million over the same period resulting in a decrease of $32.7 million in the net balance of unbilled services and unearned revenue or payments on account between December 31, 2018 and December 31, 2019 . These fluctuations are primarily due to timing of payments and invoicing related to the Group's clinical trial management contracts. Billings and payments are established by contractual provisions including predetermined payment schedules which may or may not correspond to the timing of the transfer of control of the Company's services under the contract. Unbilled services arise from long-term contract when a cost-based input method of revenue recognition is applied and revenue recognized exceeds the amount billed to the customer. The bad debt expense recognized on the Group's receivables and unbilled services was $0.4 million for the twelve months ended December 31, 2019 . As of December 31, 2019 approximately $5.3 billion of revenue is expected to be recognized in the future in respect of unsatisfied performance obligations. The Company expects to recognize revenue on approximately 48% of the unrealized performance obligation over the next twelve months

Provision for Doubtful Debts

Provision for Doubtful Debts	12 Months Ended
	Dec. 31, 2019
Accounts Receivable, after Allowance for Credit Loss [Abstract]
Provision for Doubtful Debts	Provision for Doubtful Debts The Company does business with most major international pharmaceutical companies. Provision for doubtful debts at December 31, 2019 and December 31, 2018 comprises: December 31, 2019 December 31, 2018 (in thousands) Opening provision $ 8,889 $ 8,930 Amounts used during the year — (995 ) Amounts provided during the year 1,691 3,083 Amounts released during the year (3,226 ) (2,355 ) Foreign exchange 26 226 Closing provision $ 7,380 $ 8,889

Business Segment and Geographic

Business Segment and Geographical Information	12 Months Ended
	Dec. 31, 2019
Segment Reporting [Abstract]
Business Segment and Geographical Information	Business Segment and Geographical Information The Company is a clinical research organization ("CRO"), providing outsourced development services on a global basis to the pharmaceutical, biotechnology and medical device industries. It specializes in the strategic development, management and analysis of programs that support all stages of the clinical development process - from compound selection to Phase I-IV clinical studies. The Company has the expertise and capability to conduct clinical trials in most major therapeutic areas on a global basis and has the operational flexibility to provide development services on a stand-alone basis or as part of an integrated "full service" solution. The Company has expanded predominately through internal growth, together with a number of strategic acquisitions to enhance its expertise and capabilities in certain areas of the clinical development process. The Company determines and presents operating segments based on the information that is internally provided to the chief operating decision maker, the (‘CODM’) in accordance with ASC 280 'Segment Reporting' . The Company determined that the CODM was comprised of the Chief Executive Officer and the Chief Financial Officer. The Company operates as one business segment, which is the provision of outsourced development services on a global basis to the pharmaceutical, biotechnology and medical devices industries. Revenues are allocated to individual entities based on where the work is performed in accordance with the Company's global transfer pricing model. Revenues and income from operations in Ireland are a function of our global contracting model and the Group’s transfer pricing model. Given ICON Clinical Research Limited's ("ICON Ireland") role in the development and management of the Group, it's ownership of key intellectual property, customer relationships, its key role in the mitigation of risks faced by the Group, plus the responsibility for maintaining the Group's global network, ICON Ireland acts as the group entrepreneur and enters into the majority of the Company's customer contracts. As such, ICON Ireland remunerates most of the other operating entities ("cost plus service providers") in the ICON Group on the basis of a guaranteed cost plus mark-up for the services they perform in each of their local territories. The cost plus mark-up for each ICON entity is established to ensure that each of ICON Ireland and the ICON entities in the various geographical areas that are involved in the conduct of services for customers, earn an appropriate arms-length return having regard to the assets owned, risks borne and functions performed by each entity from these intercompany transactions. The cost plus mark-up policy is reviewed annually to ensure that it is market appropriate. Under this method, the residual operating profits (or losses) of the Group, once the cost plus service providers have been paid their respective intercompany service fee, are retained by ICON Ireland. The geographic split of revenue disclosed for each region outside Ireland is the cost plus revenue attributable to these entities. The revenues disclosed as relating to Ireland are the net revenues after deducting the cost plus revenues attributable to the activities performed outside Ireland. The Company's areas of operation outside of Ireland include the United States, United Kingdom, Belgium, Bulgaria, France, Germany, Italy, Spain, Poland, Portugal, Czech Republic, Hungary, Israel, Latvia, Romania, Russia, Serbia, Sweden, The Netherlands, Turkey, Ukraine, Canada, Mexico, Argentina, Brazil, Chile, Colombia, Peru, India, China (including Hong Kong), Japan, Singapore, South Korea, The Philippines, Taiwan, Thailand, Australia, New Zealand, and South Africa. There have been no changes to the basis of segmentation or the measurement basis for the segment results since the prior year. Reportable segment information at December 31, 2019 and December 31, 2018 and for the years ended December 31, 2019 , December 31, 2018 and December 31, 2017 is as follows: a) The distribution of revenue by geographical area was as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 Restated* (in thousands) Ireland $ 1,252,834 $ 1,066,200 $ 944,130 Rest of Europe 388,916 379,883 355,552 U.S. 892,497 894,978 881,829 Other 271,592 254,716 220,810 Total $ 2,805,839 $ 2,595,777 $ 2,402,321 * 2017 restated to reflect gross revenue. b) The distribution of income from operations, including restructuring and other items, by geographical area was as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Ireland $ 314,287 $ 257,089 $ 232,032 Rest of Europe 37,997 36,280 26,493 U.S. 60,272 58,561 58,322 Other 20,850 21,427 21,491 Total $ 433,406 $ 373,357 $ 338,338 c) The distribution of income from operations, excluding restructuring and other items, by geographical area was as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Ireland $ 314,287 $ 269,196 $ 240,115 Rest of Europe 37,997 36,904 26,351 U.S. 60,272 58,340 58,164 Other 20,850 21,407 21,461 Total $ 433,406 $ 385,847 $ 346,091 d) The distribution of long-lived assets (including right-of-use assets (year ended December 31, 2019 only)), net, by geographical area was as follows: December 31, 2019 December 31, 2018 (in thousands) Ireland $ 110,522 $ 106,206 Rest of Europe 41,970 9,807 U.S. 72,578 25,535 Other 44,994 17,121 Total $ 270,064 $ 158,669 e) The distribution of depreciation, amortization and reduction in carrying value of the right-of-use assets (year ended December 31, 2019 only) by geographical area was as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Ireland $ 30,635 $ 34,721 $ 26,277 Rest of Europe 14,370 5,331 6,857 U.S. 33,922 21,605 24,246 Other 12,995 4,259 3,917 Total $ 91,922 $ 65,916 $ 61,297 f) The distribution of total assets by geographical area was as follows: Year Ended December 31, 2019 December 31, 2018 (in thousands) Ireland $ 1,323,181 $ 1,073,411 Rest of Europe 660,797 514,010 U.S. 755,271 646,512 Other 168,263 120,322 Total $ 2,907,512 $ 2,354,255 g) The distribution of capital expenditures (including right-of-use assets (year ended December 31, 2019 only)) by geographical area was as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Ireland $ 32,526 $ 30,942 $ 24,468 Rest of Europe 13,971 2,590 2,819 U.S. 18,638 9,311 11,027 Other 15,010 5,554 6,403 Total $ 80,145 $ 48,397 $ 44,717 h) The following table sets forth the clients which represented 10% or more of the Company's revenue in each of the periods set out below. Year ended December 31, 2019 December 31, 2018 December 31, 2017 Client A 12 % 14 % 21 % Client B 10 % — % — % i) The distribution of interest income by geographical area was as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Ireland $ 3,674 $ 2,620 $ 1,084 Rest of Europe 2,242 1,750 1,222 U.S. 111 17 16 Other 832 372 24 Total $ 6,859 $ 4,759 $ 2,346 j) The distribution of the income tax charge by geographical area was as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Ireland $ 38,788 $ 29,096 $ 20,345 Rest of Europe 4,234 (434 ) 1,921 U.S. 1,571 3,761 14,772 Other 6,540 9,535 9,531 Total $ 51,133 $ 41,958 $ 46,569

Supplemental Disclosure of Cash

Supplemental Disclosure of Cash Flow Information	12 Months Ended
	Dec. 31, 2019
Supplemental Cash Flow Elements [Abstract]
Supplemental Disclosure of Cash Flow Information	Supplemental Disclosure of Cash Flow Information Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Cash paid for interest $ 13,059 $ 13,060 $ 13,094 Cash paid for income taxes (net of refunds) $ 29,836 $ 18,558 $ 12,305

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income	12 Months Ended
	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income	Accumulated Other Comprehensive Income Year ended December 31, 2019 December 31, 2018 (in thousands) Currency translation adjustments $ (64,023 ) $ (62,710 ) Currency impact on long term funding (7,726 ) (5,016 ) Actuarial loss on defined benefit pension plan (note 9) (5,226 ) (3,000 ) Unrealized capital gain – investments (note 3) 231 (450 ) Realized gain on interest rate hedge 4,658 4,658 Amortization of interest rate hedge (3,733 ) (2,810 ) Total $ (75,819 ) $ (69,328 )

Operating Leases

Operating Leases	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Operating Leases	Operating leases Lease costs recorded under operating leases for the year ended December 31, 2019 were as follows: Year ended December 31, 2019 Operating lease costs $ 34,759 Income from sub-leases (1,761 ) Net operating lease costs $ 32,998 Of the total cost of $33.0 million incurred in the year ended December 31, 2019 , $30.5 million is recorded within selling, general and administration costs and $2.5 million is recorded within direct costs. During the year ended December 31, 2019 , the Group did no t incur any costs related to variable lease payments. The adoption of ASC 842 resulted in the recognition of operating right-of-use assets and lease liabilities of $106.5 million at January 1, 2019. Additional right-of-use assets obtained in exchange for lease obligations during the year ended December 31, 2019 totaled $29.5 million . The weighted average remaining lease term and weighted-average discount rate at December 31, 2019 were 5.19 years and 2.91% , respectively. Future minimum lease payments under non-cancelable leases as of December 31, 2019 were as follows: Minimum rental payments (in thousands) 2020 $ 28,320 2021 25,315 2022 19,433 2023 14,053 2024 8,839 Thereafter 17,264 Total future minimum lease payments 113,224 Lease imputed interest (8,311 ) Total $ 104,913 Operating lease liabilities are presented as current and non-current. Operating lease liabilities of $28.3 million have been included in other liabilities as at December 31, 2019 .

Debt - Senior Notes

Debt - Senior Notes	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Debt - Senior Notes	Debt – Senior Notes In December 2015 the Company issued $350 million in the private placement market which is due for repayment in 2020. The interest rate in respect of these Senior Notes is fixed at 3.64% for the five year term. The interest cost is recognized in interest expense in the period since drawdown in December 2015. In October 2015 , the Company entered into an interest rate hedge in respect of the planned issuance of the Senior Notes in December 2015. The interest rate hedge matured in November 2015 when the interest rate on the Senior Notes was fixed. The interest rate hedge was effective in accordance with ASC 815 'Derivatives and Hedging' . The cash proceeds ( $4.6 million ), representing the realized gain on the interest rate hedge, were received on maturity in November 2015 and are recorded within Other Comprehensive Income. The realized gain is being amortized to the Consolidated Statements of Operations over the term of the Senior Notes (net against interest payable). The Senior Notes agreement also includes certain financial covenants that require compliance with a consolidated leverage ratio, a minimum EBIT to consolidated net interest charge ratio and a maximum amount of priority debt, each of which are defined in the Note Purchase and Guarantee Agreement. The Company was in compliance with these covenants at December 31, 2019 . The Senior Notes have not been registered under the Securities Act of 1933, as amended, and may not be offered or sold in the United States absent registration or an applicable exemption from registration requirements. We regularly evaluate our financing arrangements and related market conditions. We are evaluating the opportunity to extend or modify our existing arrangements or pursue additional financing arrangements that may result in the issuance of new debt securities by us or our affiliates. Cash and short-term investments were $569.9 million

Impact of New Accounting Pronou

Impact of New Accounting Pronouncements	12 Months Ended
	Dec. 31, 2019
Accounting Changes and Error Corrections [Abstract]
Impact of New Accounting Pronouncements	Impact of New Accounting Pronouncements Impact of new accounting pronouncements adopted during fiscal year ended December 31, 2019 Leases The Company adopted ASC 842 'Leases' (ASC 842) with a date of initial application of January 1, 2019. The lease accounting policy applied in preparation of the results for the twelve months ended December 31, 2019 therefore reflect application of ASC 842. ICON adopted the standard using the cumulative-effect adjustment approach. Under this transition method, ICON has applied the new standard as at the date of initial application (i.e. January 1, 2019), without restatement of comparative period amounts. The cumulative effect of applying the new standard is recorded as an adjustment to the opening Consolidated Balance Sheet as at the date of initial application (see note 28 - Impact of change in accounting policies ). The comparative information has not been adjusted and therefore the results for the years ended December 31, 2018 and December 31, 2017 continue to be reported under ASC 840 'Leases' (ASC 840). The new standard requires lessees to recognize the rights and obligations resulting from virtually all leases on the balance sheet as right-of-use (ROU) assets with corresponding lease liabilities. The most significant impact of application of the new standard for ICON relates to the recognition of ROU assets and lease liabilities on the Consolidated Balance Sheets for operating leases for certain property, vehicles and equipment. Prior to application of ASC 842, costs in respect of operating leases were charged to the Consolidated Statements of Operations on a straight-line basis over the lease term. A lease liability and ROU asset have been recorded on the Consolidated Balance Sheet as at January 1, 2019 of $106.5 million (see note 28 - Impact of change in accounting policies ). The net operating cost of leases recorded in the year ended December 31, 2019 is $33.0 million (see note 22 - Operating leases ). Pursuant to certain practical expedients available as part of adopting ASC 842, ICON has not reassessed; whether existing or expired contracts are or contain leases, the classification of existing or expired leases, or whether unamortized initial direct costs meet the new definition of initial direct costs under ASC 842. Additionally, ICON has elected to use hindsight in determining the lease term and in assessing impairment of ROU assets, if any. ICON determines if an arrangement is a lease at inception. Finance leases, if any, are depreciated on the same basis as property, plant and equipment. At December 31, 2019 and December 31, 2018 , the Group did not account for any leases as finance leases. Operating leases are included in operating ROU assets, other liabilities and non-current operating lease liabilities on our Consolidated Balance Sheets with the lease charge recognized on a straight-line basis over the lease term. ROU assets and lease liabilities are recognized based on the present value of future minimum lease payments over the lease term at commencement date or date of transition. Our lease terms may also include options to extend or terminate. ICON actively reviews options to extend or terminate leases and adjusts the ROU asset and lease liability when it is reasonably certain the option will be exercised. The ROU asset is adjusted for any prepayments made at the date of commencement and any initial direct costs incurred. As most of ICON's leases do not provide an implicit rate, the discount rate used is based on the rate of traded corporate bonds available at the commencement date adjusted for country risk, liquidity and lease term. Leasehold improvements are amortized over the shorter of the depreciable lives of the corresponding fixed assets or the lease term including any applicable renewals. Certain property leases include variable lease payments resulting from periodic rent increases based on an index which are recognized as incurred in the Consolidated Statements of Operations. ICON accounts for lease and non-lease components separately with lease components flowing through the Consolidated Balance Sheets and non-lease components expensed directly to the Consolidated Statements of Operations. Other We have reviewed the FASB issued Accounting Standards Update (ASU) accounting pronouncements and interpretations thereof that have effective dates during the periods reported. The following relevant ASUs have also been adopted in 2019: In August 2017, the FASB issued ASU 2017-12 'Derivatives and Hedging - Targeted Improvements to Accounting for Hedging Activities (Topic 815)' . The updated guidance expands an entity’s ability to hedge nonfinancial and financial risk components and reduce complexity in fair value hedges of interest rate risk. The guidance eliminates the requirement to separately measure and report hedge ineffectiveness and generally requires the entire change in the fair value of a hedging instrument to be presented in the same income statement line as the hedged item. The guidance also eases certain documentation and assessment requirements and modifies the accounting for components excluded from the assessment of hedge effectiveness. Entities will apply the amendments to cash flow and net investment hedge relationships that exist on the date of adoption using a modified retrospective approach. The presentation and disclosure requirements apply prospectively. This ASU was effective for public business entities, for annual and interim periods in fiscal years beginning after December 15, 2018. The adoption of this ASU did not have a significant impact on the financial statements. In July 2017, the FASB issued ASU 2017-11 'Earnings Per Share (Topic 260); Distinguishing Liabilities from Equity (Topic 480); Derivatives and Hedging (Topic 815): (Part I) Accounting for Certain Financial Instruments with Down Round Features, (Part II) Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception' under which down round features will not cause certain equity-linked financial instruments to be accounted for as derivatives. A company that presents EPS information will reflect the effect of a down round feature of free-standing equity-linked financial instruments in EPS only if it is triggered. The ASU was effective for public business entities, for annual and interim periods in fiscal years beginning after December 15, 2018. The adoption of this ASU did not impact on the financial statements. In January 2017, the FASB issued ASU 2017-04 'Intangibles - Goodwill and Other: Simplifying the test for goodwill impairment' which requires an entity to no longer perform a hypothetical purchase price allocation to measure goodwill impairment. Instead, impairment will be measured using the difference between the carrying amount and the fair value of the reporting unit. The ASU is effective for public businesses, that are SEC filers, for annual and interim periods in fiscal years beginning after December 15, 2019, with early adoption permitted. The Company early adopted this ASU from 1 January 2018. The adoption of this ASU did not have a significant impact on the financial statements. In July 2018, the FASB issued ASU 2018-09 'Codification Improvements' . This amendment makes changes to a variety of topics to clarify, correct errors in, or make minor improvements to the Accounting Standards Codification (ASC). The transition and effective date guidance is based on the facts and circumstances of each amendment. Some of the amendments do not require transition guidance and will be effective upon issuance of ASU 2018-09. The amendments effective upon issuance did not have a material impact on the Company's consolidated financial statements. A majority of the amendments do have transition guidance with effective dates for annual periods beginning after December 15, 2018. The adoption of this ASU did not have a significant impact on the financial statements. In June 2018, the FASB issued ASU 2018-07, which expands the scope of ASC 718 'Compensation—Stock Compensation' (ASC 718) to include share based payment transactions for acquiring goods and services from nonemployees and more closely aligns the accounting for employee and nonemployee share-based payments. This ASU was effective for public business entities for annual and interim periods in fiscal years beginning after December 15, 2018. The adoption of this ASU did not impact on the financial statements. In February 2018, the FASB issued ASU 2018-02, which allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act. This ASU was effective for all entities for annual and interim periods in fiscal years beginning after December 15, 2018. The adoption of this ASU did not have a significant impact on the financial statements. In February 2018, the FASB issued ASU 2018-03, which provided technical corrections and improvements to ASU No. 2016-01 'Financial Instruments—Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities' . The amendments clarify certain aspects of the guidance issued in update 2016-01. The ASU was effective for public business entities for fiscal years beginning after December 15, 2017. The adoption of this ASU did not have a significant impact on the financial statements. Impact of new accounting pronouncements which will be adopted during fiscal year ended December 31, 2020 In June 2016, the FASB issued ASU 2016-13 'Measurement of Credit Losses on Financial Instruments (Topic 326)' , which significantly changes the way entities recognize impairment of many financial assets by requiring immediate recognition of estimated credit losses expected to occur over their remaining life. The update provides guidance on the measurement of credit losses for most financial assets and certain other instruments that are not measured at fair value through net income. The amendment replaces the current incurred loss impairment approach with a methodology to reflect expected credit losses and requires consideration of a broader range of reasonable and supportable information to explain credit loss estimates. The updated guidance is to be applied on a modified retrospective approach and is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019 for public business entities that are SEC filers. The adoption of Topic 326 is not expected to have a significant impact on the financial statements. In August 2018, the FASB issued ASU No. 2018-15 'Intangibles - Goodwill and Other - Internal-Use Software: Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (Topic 350) '. The amendments in the update align the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). The ASU is effective for public businesses, that are SEC filers for fiscal years beginning after December 15, 2019, and for interim periods within those fiscal years and is to be applied either retrospectively or prospectively to all implementation costs incurred after the adoption date. The adoption of ASU 2018-15 is not expected to have a significant impact on the financial statements. In August 2018, the FASB issued ASU 2018-13 'Fair Value Measurement - Disclosure Framework (Topic 820)' . The updated guidance requires entities to disclose changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements and the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. Amendments in this guidance also require disclosure of transfers into and out of Level 3 of the fair value hierarchy, purchases and issues of Level 3 assets and liabilities, and clarify that the measurement uncertainty disclosure is about the uncertainty in measurement as of the reporting date. The guidance removes requirements to disclose the amounts and reasons for transfers between Level 1 and Level 2, policy for timing between of transfers between levels, and the valuation processes for Level 3 fair value measurements. The updated guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted for any removed or modified disclosures. The adoption of ASU 2018-13 is not expected to have a significant impact on the financial statements. In November 2019, the FASB issued ASU 2019-08 'Codification Improvements—Share-Based Consideration Payable to a Customer' . The amendments in this update require that an entity measure and classify share-based payment awards granted to a customer by applying the guidance in ASC 718. The amount recorded as a reduction of the transaction price is required to be measured on the basis of the grant-date fair value of the share-based payment award in accordance with ASC 718. The grant date is the date at which a grantor (supplier) and a grantee (customer) reach a mutual understanding of the key terms and conditions of a share-based payment award. The classification and subsequent measurement of the award are subject to the guidance in ASC 718 unless the share-based payment award is subsequently modified and the grantee is no longer a customer. The amendments in this update are effective for public business entities in fiscal years beginning after December 15, 2019. The adoption of ASU 2019-08 is not expected to have a significant impact on the financial statements. Impact of other new accounting pronouncements In August 2018, the FASB issued ASU 2018-14 'Compensation - Retirement Benefits - Defined Benefit Plans (Topic 715)'. The updated guidance requires additional disclosures of weighted-average interest crediting rates for cash balance plans and an explanation of the reasons for significant gains and losses related to changes in the benefit obligation. Amendments in the guidance also clarify the requirement to disclose the projected benefit obligation (PBO) and fair value of plan assets for plans with PBOs in excess of plan assets. The same disclosure is needed for the accumulated benefit obligation (ABO) and fair value of plan assets for plans with ABOs in excess of plan assets. The guidance removes certain previous disclosure requirements no longer considered cost beneficial. The amendments are effective for fiscal years ending after December 15, 2020, with early adoption permitted. The Company is currently assessing the impact of adopting the updated provisions. In December 2019, the FASB issued ASU 2019-12 'Simplifying the Accounting for Income Taxes (Topic 740)'. The amendments in this update simplify the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The amendments also improve consistent application of GAAP for other areas of Topic 740 by clarifying and amending existing guidance. The Company is currently assessing the impact of adopting the updated provisions. No other new accounting pronouncement issued or effective has had, or is expected to have, a material impact on the Company’s consolidated financial statements.

Related Parties

Related Parties	12 Months Ended
	Dec. 31, 2019
Related Party Transactions [Abstract]
Related Parties	Related Parties Subsidiaries of the Company earned revenue of $95,000 ( December 31, 2018 : $633,000 ) from DS Biopharma Limited (formerly Dignity Sciences Limited) during the year. Dr. John Climax is Chief Executive Officer and both Dr. John Climax and Dr. Ronan Lambe are Directors and shareholders of DS Biopharma Limited. $36,000 was recorded as due from DS Biopharma Limited at December 31, 2019 ( December 31, 2018 : $338,000 ). Dr Ronan Lambe resigned as a Director of ICON plc on July 24, 2018. The contract terms were agreed on an arm’s length basis. During the year ended December 31, 2017, personal expenses totaling $178,000 were settled by the Company on behalf of Mr. Ciaran Murray. Payment was received in advance from Mr. Murray in respect of these expenses. The Company transferred ownership of an asset at fair value ( $77,000 ) to Mr. Ciaran Murray effective November 1, 2017. Payment was received in full in January 2018. On July 22, 2016, Mr. Thomas Lynch retired as a Director of the Company, having previously resigned as Chairman of the Company in March 2016. The terms of the consultancy agreement expired on July 31, 2019. A charge of $151,360 was recorded during 2019 in respect of consultancy services provided by a company controlled by Mr. Lynch ( December 31, 2018 : $274,519 ). There were no amounts due to Mr. Lynch at December 31, 2019 ( December 31, 2018 : $64,000

Net Income Per Ordinary Share (

Net Income Per Ordinary Share (Notes)	12 Months Ended
	Dec. 31, 2019
Earnings Per Share [Abstract]
Net Income Per Ordinary Share	Net income per ordinary share Basic net income per ordinary share attributable to the Group has been computed by dividing net income available to ordinary shareholders by the weighted average number of ordinary shares outstanding during the period. Diluted net income per ordinary share is computed by adjusting the weighted average number of ordinary shares outstanding during the period for all potentially dilutive ordinary shares outstanding during the period and adjusting net income for any changes in income or loss that would result from the conversion of such potential ordinary shares. There is no difference in net income used for basic and diluted net income per ordinary share. Basic and diluted net income per ordinary share attributable to the Group includes the adjustment to reflect the accretion of the noncontrolling interest in MeDiNova to its redemption value. The reconciliation of the number of shares used in the computation of basic and diluted net income per ordinary share is as follows: December 31, 2019 December 31, 2018 December 31, 2017 Weighted average number of ordinary shares outstanding for basic net income per ordinary share 53,859,537 54,118,764 54,129,439 Effect of dilutive share options outstanding 473,924 671,899 719,607 Weighted average number of ordinary shares outstanding for diluted net income per ordinary share 54,333,461 54,790,663 54,849,046 The reconciliation between net income attributable to the Group per the Statement of Operating Income and the net income used to calculate net income per ordinary share attributable to the Group is as follows: December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Net income attributable to the Group $ 373,986 322,656 $ 281,488 Noncontrolling interest adjustment to redemption amount (5,048 ) — — Net income attributable to the Group (including NCI redemption adjustment) 368,938 322,656 281,488 December 31, 2019 December 31, 2018 December 31, 2017 Net income per Ordinary Share attributable to the Group (including NCI redemption adjustment): Basic $ 6.85 $ 5.96 $ 5.20 Diluted $ 6.79 $ 5.89 $ 5.13

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2019
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On January 22, 2020 a subsidiary of the Company, ICON Investments Limited acquired 100% of the equity share capital of MedPass International ("MedPass"). The initial consideration on acquisition is $39.2 million . The opening balance sheet remains under preparation and our initial estimate of the net assets of MedPass is approximately $9.2 million . MedPass is the leading European medical device CRO, regulatory and reimbursement consultancy, that specializes in medical device development and market access. The acquisition of MedPass further enhances ICON’s Medical Device and Diagnostic Research Services, through the addition of new regulatory and clinical capabilities in Europe. The integration of MedPass’s services brings noted expertise in complex class 3 medical devices, interventional cardiology and structural heart devices . On January 14, 2020, the Company announced the intention to buyback up to 1.0 million shares during 2020 depending on cash commitments. All ordinary shares that are redeemed under the buyback program will be canceled in accordance with the constitutional documents of the Company and the nominal value of these shares transferred to an undenominated capital fund as required under Irish Company law.

Impact of Change in Accounting

Impact of Change in Accounting Policies	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Impact of Change in Accounting Policies	Impact of change in accounting policies Leases The new leasing standard (ASU No. 2016-02 ' Leases ') was issued in February 2016. ASC 842 ' Leases ' (ASC 842) supersedes the requirements in ASC 840 ' Leases ' (ASC 840) and requires that lessees recognize rights and obligations from virtually all leases (other than leases that meet the definition of a short-term lease) on their Balance Sheets as right-of-use assets with corresponding lease liabilities. The ASU also provides additional guidance on how to classify leases and how to determine the lease term for accounting purposes. In July 2018, the FASB issued ASU No. 2018-11 ' Leases (Topic 842): Targeted Improvements ', which provides the option to adopt the standard retrospectively for each prior period presented, as initially set out in ASU No. 2016-02, or as of the adoption date with a cumulative-effect adjustment to the opening balance of retained earnings. ASC 842 became effective for ICON plc with effect from January 1, 2019. ICON adopted the new standard as of January 1, 2019 under the cumulative effect adjustment approach. Under this transition method, the new standard is applied from January 1, 2019 without restatement of comparative period amounts. Results for the years ended December 31, 2018 and December 31, 2017 are therefore presented under the previous leasing accounting principles, ASC 840. Operating lease liabilities and right-of-use assets have been recorded on the Consolidated Balance Sheets as at January 1, 2019 of $106.5 million . There is no impact of adopting ASC 842 on opening retained earnings at January 1, 2019. Revenue In the previous financial year, the Company adopted ASC 606 'Revenue from Contracts with Customers' (ASC 606) on January 1, 2018. The new revenue recognition policies were applied in the preparation and presentation of the results for the twelve months ended December 31, 2018 and the twelve months ended December 31, 2019. As ICON adopted the standard using the cumulative effect transition method, there was no restatement of comparative amounts. Therefore, the results for the year ended December 31, 2017 and previously reflect the provisions of ASC 605 'Revenue Recognition' . The most significant impact of application of the new standard was the measurement of a clinical trial service as a single performance obligation recognized over time. We concluded that ICON is the contract principal in respect of both direct services and in the use of third parties (principally investigator services) that support the clinical trial. The progress towards completion for clinical service contracts is measured based on total project costs (direct fees are therefore inclusive of third party costs). Revenue is our primary measure of performance on adoption of ASC 606. In common with others in the sector, our results previously separately identified that revenue stream which related to services provided by third parties. Those services were previously separately identified as reimbursable expenses and presented separately in our Consolidated Statements of Operations. Reimbursable expenses are included within direct costs on adoption of ASC 606. Throughout the document revenue as reported on adoption of ASC 606 is referred to as revenue. Revenue as reported for the years ended December 31, 2017 and previously are gross revenues (inclusive of revenue from reimbursable expenses) or net revenues (exclusive of revenue from reimbursable expenses). This treatment is consistent with the adoption of ASC 606 from January 1, 2018 without restatement of comparatives. Incremental costs of obtaining a contract were also considered on adoption of ASC 606. Commission costs of $12 million were recognized as an asset on the Consolidated Balance Sheet in respect of those contracts that exceed one year. Where commission costs relate to contracts that are less than one year, the practical expedient is applied as the amortization period of the asset which would arise on deferral would be one year or less.

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Basis of Consolidation	Basis of consolidation The consolidated financial statements include the financial statements of the Company and all of its subsidiaries. All significant intercompany profits, transactions and account balances have been eliminated. The results of subsidiary undertakings acquired in the period are included in the Consolidated Statement of Operations from the date of acquisition.
Use of Estimates	Use of estimates The preparation of financial statements in conformity with generally accepted accounting principles in the United States requires management to make estimates and judgments 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 reported period. Actual results could differ from those estimates. The principal management estimates and judgments used in preparing the financial statements relate to revenue recognition and taxation.
Revenue Recognition	Revenue recognition The Company primarily earns revenues by providing a number of different services to its customers. These services, which are integral elements of the clinical development process, include clinical trials management, consulting, contract staffing, and laboratory services. Contracts range in duration from a number of months to several years. ASC 606 - Revenue from Contracts with Customers (years ended December 31, 2019 and December 31, 2018) ICON adopted ASC 606 'Revenue from Contracts with Customers ' (ASC 606) standard using the cumulative effect transition method for the first time in the year ended December 31, 2018. Under this transition method, ICON applied the new standard as at the date of initial application (i.e. January 1, 2018), without restatement of comparative amounts. The cumulative effect of initially applying the new standard (to revenue, costs and tax) was recorded as an adjustment to the opening balance of equity at the date of initial application. The comparative information, for the year ended December 31, 2017 is not adjusted and therefore continues to be reported under ASC 605 ‘Revenue Recognition’ (ASC 605) and therefore in accordance with previous accounting policies. The new standard requires application of five steps: (1) identify the contract(s) with a customer; (2) identify the performance obligation in the contract; (3) determine the transaction price; (4) allocate the transaction price to the performance obligations in the contract; and (5) recognize revenue when (or as) the entity satisfies the performance obligation. Clinical trial service revenue The most significant impact of application of the standard relates to our assessment of performance and percentage of completion in respect of our clinical trial service revenue. Prior to application of ASC 606, the revenue attributable to performance was determined based on both input and output methods of measurement on a percentage of completion basis. We have concluded that under the new standard, a clinical trial service is a single performance obligation satisfied over time i.e. the full service obligation in respect of a clinical trial (including those services performed by investigators and other parties) is considered a single performance obligation. Promises offered to the customer are not distinct within the context of the contract. We have concluded that ICON is the contract principal in respect of both direct services and in the use of third parties (principally investigator services) that support the clinical research project. The transaction price is determined by reference to the contract or change order value (total service revenue and pass-through/ reimbursable expenses) adjusted to reflect a realizable contract value. Revenue is recognized as the single performance obligation is satisfied. The progress towards completion for clinical service contracts is measured based on an input measure being total project costs incurred (inclusive of third party costs) at each reporting period as a percentage of total forecast project costs. Contracting services revenue On evaluation of the principles at (1) - (5) set-out above in respect of ASC 606, the Company has availed of the practical expedient which results in recognition of revenue on a right to invoice basis. Application of the practical expedient reflects the right to consideration from the customer in an amount that corresponds directly with the value to the customer of the performance completion to date. This reflects hours performed by contract staff. Consulting services revenue On application of the ASC 606 principles at (1) - (5) set-out above, we have concluded that our consulting services contracts represent a single performance obligation satisfied over time. The transaction price is determined by reference to contract or change order value. Revenue is recognized as the performance obligation is satisfied. The progress towards completion for consulting contracts is measured based on total project inputs (time) at each reporting period. Laboratory services revenue Revenue is recognized when, or as, obligations under the terms of a contract are satisfied, which occurs when control of the products or services are transferred to the customer. Revenue for laboratory services is measured as the amount of consideration we expect to receive in exchange for transferring products or services. Where contracts with customers contain multiple performance obligations, the transaction price is allocated to each performance obligation based on the estimated relative selling price of the promised good or service. Service revenue is recognized over time as the services are delivered to the customer based on the extent of progress towards completion of the performance obligation. The determination of the methodology to measure progress requires judgment and is based on the nature of services provided. This requires an assessment of the transfer of value to the customer. The right to invoice measure of progress is generally related to rate per unit contracts, as the extent of progress towards completion is measured based on discrete service or time-based increments, such as samples tested or labor hours incurred. Revenue is recorded in the amount invoiced since that amounts corresponds to the value of the Company's performance and the transfer of value to the customer. Commissions Incremental costs of obtaining a contract were also considered on adoption of ASC 606. Commission costs of $12 million were recognized as an asset on the Consolidated Balance Sheet on application of ASC 606 in respect of those contracts that exceed one year. Where commission costs relate to contracts that are less than one year, the practical expedient is applied as the amortization period of the asset which would arise on deferral would be one year or less. ASC 605 - Revenue recognition (year ended December 31, 2017) Revenue for services, as rendered, is recognized only after persuasive evidence of an arrangement exists, the sales price is fixed or determinable and collectability is reasonably assured. Clinical trials management revenue is recognized on a proportional performance method. Depending on the contractual terms revenue is either recognized on the percentage of completion method based on the relationship between hours incurred and the total estimated hours of the trial or on the unit of delivery method. Contract costs equate to the product of labor hours incurred and compensation rates. For the percentage of completion method, the input (effort expended) method has been used to measure progress towards completion as there is a direct relationship between input and productivity. Contract revenue is the product of the aggregated labor hours required to complete the specified contract tasks at the agreed contract rates. The Company regularly reviews the estimate of total contract time to ensure such estimates remain appropriate taking into account actual contract stage of completion, remaining time to complete and any identified changes to the contract scope. Remaining time to complete depends on the specific contract tasks, the complexity of the contract and can include geographical site selection and initiation, patient enrollment, patient testing and level of results analysis required. While the Company may routinely adjust time estimates, the Company's estimates and assumptions historically have been accurate in all material respects in the aggregate. Where revenue is recognized on the unit of delivery method, the basis applied is the number of units completed as a percentage of the total number of contractual units. Consulting revenue is recognized on a fee-for-service basis as each hour of the related service is performed. Contract staffing revenue is recognized on a fee-for-service basis, over the time the related service is performed. Laboratory service revenue is recognized on a fee-for-service basis. The Company accounts for laboratory service contracts as multiple element arrangements, with contractual elements comprising laboratory kits and laboratory testing, each of which can be sold separately. Sales prices for contractual elements are determined by reference to objective and reliable evidence of their sales price. Revenues for contractual elements are recognized on the basis of the number of deliverable units completed in the period. License and support fee revenues are recognized rateably over the period of the related agreement. Revenue from software services is recognized using the percentage of completion method based on the relationship between hours incurred and the total estimated hours required to perform the service. Contracts generally contain provisions for renegotiation in the event of changes in the scope, nature, duration, or volume of services of the contract. Renegotiated amounts are recognized as revenue by revision to the total contract value arising as a result of an authorized customer change order. (d) Third party costs (Reimbursable expenses) Reimbursable expenses comprise investigator payments and certain other costs which are reimbursed by clients under terms specific to each contract to the investigators. Third party costs (reimbursable expenses) and the related revenue were separately presented on the face of the Consolidated Statement of Operations for periods up to and including the year ended December 31, 2017. See sections (c) and (e) for accounting policy in respect of the treatment of activity relating to reimbursable expenses on revenue (c) and costs (e) on adoption of ASC 606.
Direct Costs	Direct costs Direct costs consist of compensation, associated employee benefits and share-based payments for project-related employees and other direct project-related costs. Reimbursable expenses are presented within direct costs. This presentation is to align the presentation of costs with our assessment that our clinical trial service is a single performance obligation satisfied over time i.e. the full service obligation is in respect of a clinical trial (including those services performed by investigators and other parties) is considered a single performance obligation. Reimbursable expenses are recorded once the activity which forms the basis for the cost has occurred. Investigator payment costs are recorded and reported reflecting investigator activity over the life of the contract. Investigator payments are made based on predetermined contractual arrangements. Payments may differ from the recording and reporting of the expense which is based on activity.
Advertising Costs	Advertising costs
Foreign Currencies and Translation of Subsidiaries	Foreign currencies and translation of subsidiaries
Disclosure of Fair Value of Financial Instruments	Disclosure of fair value of financial instruments Cash, cash equivalents, unbilled revenue, other receivables, available for sale investments, prepayments and other current assets, accounts receivable, accounts payable, investigator payments, payments on account/unearned revenue, accrued liabilities, accrued bonuses and income taxes payable have carrying amounts that approximate fair value due to the short term maturities of these instruments. Other liabilities' carrying amounts approximate fair value based on net present value of estimated future cash flows. Debt is measured at historical cost. Financial instruments are measured in the Consolidated Balance Sheets at fair value using a fair value hierarchy of valuation inputs. The hierarchy prioritizes the inputs into three levels based on the extent to which inputs used in measuring fair value are observable in the market. Each fair value measurement is reported in one of three levels, which is determined by the lowest level input that is significant to the fair value measurement in its entirety. These levels are: Level 1: Inputs are based upon unadjusted quoted prices for identical instruments traded in active markets. Level 2: Inputs are based upon quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active and model-based valuation techniques for which all significant assumptions are observable in the market or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3: Inputs are generally unobservable and typically reflect management’s estimates of assumptions that market participants would use in pricing the asset or liability. The Group's Senior notes (private placement debt) is carried at $350.0 million (prior to related financing costs). The carrying value at December 31, 2019 , closely approximates fair value. The Company classifies its investments in short term debt or equity investments as available for sale, as it does not actively trade such securities nor does it intend to hold them to maturity. The fair value of short term investments are represented by level 1 fair value measurements – quoted prices in active markets for identical assets. The unrealized movements in fair value are recognized in equity until disposal or sale, at which time, those unrealized movements from prior periods are recognized in Consolidated Statement of Operations. Losses other than temporary, which reduce the carrying amount below cost are recognized in Consolidated Statement of Operations.
Business Combinations	Business combinations The cost of a business combination is measured as the aggregate of the fair values at the date of exchange of assets given, liabilities incurred or assumed and equity instruments issued in exchange for control. Where a business combination agreement provides for an adjustment to the cost of the acquisition which is contingent upon future events, the amount of the estimated adjustment is recognized at the acquisition date at the fair value of the contingent consideration. Any changes to this estimate outside the measurement period will depend on the classification of the contingent consideration. If the contingent consideration is classified as equity it shall not be re-measured and the settlement shall be accounted for within equity. If the contingent consideration is classified as a liability any adjustments will be accounted for through the Consolidated Statement of Operations or Other Comprehensive Income depending on whether the liability is considered a financial instrument. The assets, liabilities and contingent liabilities of businesses acquired are measured at their fair values at the date of acquisition. In the case of a business combination which is completed in stages, the fair values of the identifiable assets, liabilities and contingent liabilities are determined at the date of each exchange transaction. When the initial accounting for a business combination is determined provisionally, any subsequent adjustments to the provisional values allocated to the identifiable assets, liabilities and contingent liabilities are made within twelve months of the acquisition date and presented as adjustments to goodwill in the reporting period in which the adjustments are determined. The Company allocates a share of net income to the noncontrolling interest holders based on percentage ownership. ICON acquired a majority ownership interest in MeDiNova. Included in the purchase agreement are put and call option arrangements with the noncontrolling interest holders that require (put option) or enable (call option) ICON to purchase the remaining minority ownership at a future date. The option is accounted for as temporary equity, which is presented separately as redeemable noncontrolling interest on the Consolidated Balance Sheet. This classification reflects the assessment that the instruments are contingently redeemable in accordance with ASC 480-10-S99 'Distinguishing Liabilities from Equity'. Redeemable noncontrolling interests are accreted to their redemption value over the period from the date of issuance to the first date on which the option is exercisable. The change in the option's redemption value is recorded against retained earnings. In a computation of earnings per share, the accretion of redeemable noncontrolling interests to their redemption value is a reduction of net income attributable to the Group. Basic and diluted net income per ordinary share attributable to the Group includes the adjustment to reflect the accretion of the noncontrolling interest to its redemption value.
Goodwill and Impairment	Goodwill and Impairment Goodwill represents the excess of the cost of acquired entities over the net amounts assigned to assets acquired and liabilities assumed. Goodwill primarily comprises acquired workforce in place which does not qualify for recognition as an asset apart from goodwill. Goodwill is stated net of any provision for impairment. The Company tests goodwill annually for any impairments or whenever events occur which may indicate impairment. The Company applied the provisions of ASU 2017-04 'Intangibles - Goodwill and Other: Simplifying the test for goodwill impairment' with effect from January 1, 2018. Under the amendment, the Company was required to perform its annual goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An impairment charge would be recognized for any amount by which the carrying amount exceeds the reporting unit's fair value up to the amount of existing goodwill. The amendment allows an entity to perform a qualitative assessment for a reporting unit to determine if the quantitative impairment test is necessary.
Intangible Assets	Intangible assets Intangible assets are amortized on a straight line basis over their estimated useful life.
Cash and Cash Equivalents	Cash and cash equivalents Cash and cash equivalents include cash and highly liquid investments with initial maturities of three months or less and are stated at cost, which approximates market value.
Investment in Debt, Equity and Other	Investments in debt, equity and other Available for sale investments The Company classifies short-term investments as available for sale in accordance with the terms of ASC 320 'Investments - Debt and Equity Securities' . Realized gains and losses are determined using specific identification. The investments are reported at fair value, with unrealized gains or losses reported in a separate component of shareholders' equity. Any differences between the cost and fair value of the investments are represented by accrued interest and unrealized gains/losses. Long term investments The Company classifies its interests in funds having considered the nature of its investment, the extent of influence over operating and financial decisions and the availability of readily determinable fair values. The Company determined that the interests in funds at December 31, 2019 meet the definition of equity securities without readily determinable fair values. Effective from January 1, 2018, the Company concluded that the interests held at December 31, 2018 and December 31, 2019 qualify for the NAV practical expedient in ASC 820 ' Fair value measurements and disclosure s'. Any increases or decreases in fair value are recognized in net income in the period. These are therefore measured at Level 3 of the fair value hierarchy.
Accounts Receivable, net	Accounts receivable, net Accounts receivable are recorded at fair value less an allowance for doubtful accounts. The allowance is an estimate based on historical collection experience, current economic and market conditions, and a review of the current status of each customer's trade accounts receivable. Account balances are written-off against the allowance when the Group determines that it is probable that the receivable will not be recovered. Where the Company enters into an agreement to sell certain portfolios of its accounts receivable balances, the sale is accounted for in accordance with ASC Topic 860 'Transfers and Servicing' (ASC 860). Agreements which result in true sales of the transferred receivables, as defined in ASC 860, which occur when receivables are transferred without recourse to ICON, are excluded from amounts reported in the Consolidated Balance Sheet. Cash proceeds received from such sales are included in operating cash flows. The associated finance costs are presented as interest expense.
Inventory	Inventory
Property, Plant and Equipment	Property, plant and equipment Property, plant and equipment is stated at cost less accumulated depreciation. Depreciation of property, plant and equipment is computed using the straight line method based on the estimated useful lives of the assets as listed below: Years Building 40 Computer equipment and software 2-8 Office furniture and fixtures 8 Laboratory equipment 5 Motor vehicles 5 Leasehold improvements are amortized using the straight line method over the estimated useful life of the asset or the lease term, whichever is shorter.
Leases	Leases The Company adopted ASC 842 'Leases' ( ASC 842), with a date of initial application of January 1, 2019. The lease accounting policy applied in preparation of the results for the year ended December 31, 2019 therefore reflect application of ASC 842. ICON adopted the standard using the cumulative-effect adjustment approach. Under this transition method, ICON has applied the new standard as at the date of initial application (i.e. January 1, 2019), without restatement of comparative period amounts. The cumulative effect of applying the new standard is recorded as an adjustment to the opening consolidated balance sheet as at the date of initial application (see note 24 - Impact of new accounting pronouncements for further details). The comparative information has not been adjusted and therefore continues to be reported under ASC 840 'Leases' (ASC 840) . The new standard requires lessees to recognize the rights and obligations resulting from virtually all leases on the Consolidated Balance Sheet as right-of-use (ROU) assets with corresponding lease liabilities. The most significant impact of application of the new standard for ICON relates to the recognition of right-of-use assets and lease liabilities on the Consolidated Balance Sheet for operating leases for certain property, vehicles and equipment. Prior to application of ASC 842, costs in respect of operating leases were charged to the Consolidated Statements of Operations on a straight-line basis over the lease term. Pursuant to certain practical expedients available as part of adopting ASC 842, ICON has not reassessed; whether existing or expired contracts are or contain leases, the classification of existing or expired leases, or whether unamortized initial direct costs meet the new definition of initial direct costs under ASC 842. Additionally, ICON has elected to use hindsight in determining the lease term and in assessing impairment of ROU assets, if any. ICON determines if an arrangement is a lease at inception. Finance leases, if any, are depreciated on the same basis as property, plant and equipment. At December 31, 2019 and December 31, 2018 , the Group did not account for any leases as finance leases. Operating leases are included in operating right-of-use assets, other liabilities and non-current operating lease liabilities on our Consolidated Balance Sheet with the lease charge recognized on a straight-line basis over the lease term. ROU assets and lease liabilities are recognized based on the present value of future minimum lease payments over the lease term at commencement date or date of transition. Our lease terms may also include options to extend or terminate. ICON actively reviews options to extend or terminate leases and adjusts the ROU asset and lease liability when it is reasonably certain the option will be exercised. The ROU asset is adjusted for any prepayments made at the date of commencement and any initial direct costs incurred. As most of ICON's leases do not provide an implicit rate, the discount rate used is based on the rate of traded corporate bonds available at the commencement date adjusted for country risk, liquidity and lease term. Leasehold improvements are amortized over the shorter of the depreciable lives of the corresponding fixed assets or the lease term including any applicable renewals. Certain property leases include variable lease payments resulting from periodic rent increases based on an index which are recognized as incurred on the Consolidated Statements of Operations. ICON accounts for lease and non-lease components separately with lease components flowing through the Consolidated Balance Sheet and non-lease components expensed directly to the Consolidated Statements of Operations. In some cases, ICON enters into sublease agreements and becomes both a lessee and a lessor for the same underlying asset. Although subleases are accounted for separately from the lease they relate to, subleases are accounted for in the same way as other leases. The lease accounting policy applied in preparation of the results for the year ended December 31, 2018 reflected the application of ASC 840. Under this accounting policy, costs in respect of operating leases are charged to the Consolidated Statement of Operations on a straight line basis over the lease term. Assets acquired under capital finance leases are included in the Consolidated Balance Sheet at the present value of the future minimum lease payments and are depreciated over the shorter of the lease term and their remaining useful lives. The corresponding liabilities are recorded in the Consolidated Balance Sheet and the interest element of the capital lease rental is charged to interest expense.
Income Taxes	Income taxes The Company applies the asset and liability method of accounting for income taxes. Under the asset and liability method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and for operating loss and tax credit carry-forwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which these temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. Deferred tax assets are reduced by a valuation allowance to the amount more likely than not to be realized. The Company recognizes the effect of income tax positions only if those positions will more likely than not be sustained. Recognized income tax positions are measured at the largest amount of tax benefit that is greater than 50 percent likely of being realized upon settlement. Interest and penalties related to income taxes are included in income tax expense and classified with the related liability on the Consolidated Balance Sheet. The Company accounts for the impact of GILTI (“global intangible low-taxed income”) as a period item in the period it arises and has therefore not provided for deferred taxes in respect of this item.
Government Grants	Government grants Government grants received relating to capital expenditures are shown as deferred income and credited to income on a basis consistent with the depreciation policy of the relevant assets. Grants relating to categories of operating expenditures are credited to income in the period in which the expenditure to which they relate is charged. Under the grant agreements amounts received may become repayable in full should certain circumstances specified within the grant agreements occur, including downsizing by the Company, disposing of the related assets, ceasing to carry on its business or the appointment of a receiver over any of its assets. The Company has not recognized any loss contingency having assessed as remote the likelihood of these events arising.
Research and Development Credits	Research and development credits Research and development credits are available to the Company under the tax laws in certain jurisdictions, based on qualifying research and development spend as defined under those tax laws. Research and development credits are generally recognized as a reduction of income tax expense. However, certain tax jurisdictions provide refundable credits that are not wholly dependent on the Company's ongoing income tax status or income tax position. In these circumstances the benefit of these credits is not recorded as a reduction to income tax expense, but rather as a reduction of operating expenditure.
Pension Costs	Pension costs The Company contributes to defined contribution plans covering all eligible employees. The Company contributes to these plans based upon various fixed percentages of employee compensation and such contributions are expensed as incurred. The Company operates, through two subsidiaries, a defined benefit plan for certain of its United Kingdom and Swiss employees. The Company accounts for the costs of these plans in accordance with ASC 715-30 'Defined Benefit Plans – Pension' . These plans are presented in accordance with the requirements of ASC 715-60 'Defined Benefit Plans – Other Postretirement' .
Net Income per Ordinary Share	Net income per ordinary share Basic net income per ordinary share attributable to the Group has been computed by dividing net income available to ordinary shareholders by the weighted average number of ordinary shares outstanding during the period. Diluted net income per ordinary share is computed by adjusting the weighted average number of ordinary shares outstanding during the period for all potentially dilutive ordinary shares outstanding during the period and adjusting net income for any changes in income or loss that would result from the conversion of such potential ordinary shares. There is no difference in net income used for basic and diluted net income per ordinary share. Basic and diluted net income per ordinary share attributable to the Group includes the adjustment to reflect the accretion of the noncontrolling interest in MeDiNova to its redemption value (see note 26 - Net income per ordinary share ).
Share-Based Compensation	Share-based compensation The Company accounts for its share options, Restricted Share Units ("RSUs") and Performance Share Units ("PSUs") in accordance with the provisions of ASC 718 'Compensation – Stock Compensation'. Share-based compensation expense for equity-settled awards made to employees and directors is measured and recognized based on estimated grant date fair values. These equity-settled awards include employee share options, RSUs and PSUs. Share-based compensation expense for share options awarded to employees and directors is estimated at the grant date based on each option's fair value as calculated using the Black-Scholes option-pricing model. Share-based compensation for RSUs and PSUs awarded to employees and directors is calculated based on the market value of the Company's shares on the date of award of the RSUs and PSUs. The value of awards expected to vest is recognized as an expense over the requisite service periods. Forfeitures are estimated on the date of grant and revised if actual or expected forfeiture activity differs materially from original estimates. Estimating the grant date fair value of share options as of the grant date using an option-pricing model, such as the Black-Scholes model, is affected by the Company's share price as well as assumptions regarding a number of complex variables. These variables include, but are not limited to, the expected share price volatility over the term of the awards, risk-free interest rates and the expected term of the awards.
Impairment of Long-Lived Assets	Impairment of long-lived assets Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of the asset to future undiscounted net cash flows expected to be generated by the asset. If such assets are considered to be impaired, the impairment to be recognized is measured at the amount by which the carrying amount of the asset exceeds the fair value of the asset. Assets to be disposed of are reported at the lower of the carrying amount of the asset or fair value less selling costs.
Derivative Financial Instruments	Derivative financial instruments We enter into transactions in the normal course of business using various financial instruments in order to hedge against exposure to fluctuating exchange and interest rates. We use derivative financial instruments to reduce exposure to fluctuations in interest rates. A derivative is a financial instrument or other contract whose value changes in response to some underlying variable, which has an initial net investment smaller than would be required for other instruments that have a similar response to the variable and that will be settled at a future date. We do not enter into derivative financial instruments for trading or speculative purposes. We did not hold any interest rate swap contracts or forward currency contracts at December 31, 2019 or December 31, 2018 . We use derivative financial instruments to reduce exposure to fluctuations in foreign exchange rates. During the years ended December 31, 2018 and December 31, 2019 we entered into forward currency contracts in respect of identified exposure arising from euro payments. All contracts expired during the year in which the contract was entered into. Our accounting policies for derivative financial instruments are based on whether they meet the criteria for designation as cash flow or fair value hedges. A designated hedge of the exposure to variability in the future cash flows of an asset or a liability, or of a forecast transaction, is referred to as a cash flow hedge. A designated hedge of the exposure to changes in fair value of an asset or a liability is referred to as a fair value hedge. The criterion for designating a derivative as a hedge includes the assessment of the instrument's effectiveness in risk reduction, matching of the derivative instrument to its underlying transaction and the probability that the underlying transaction will occur. For derivatives with cash flow hedge accounting designation, we report the gain or loss from the effective portion of the hedge as a component of Other Comprehensive Income and reclassify it into earnings in the same period or periods in which the hedged transaction affects earnings and within the same Consolidated Statement of Operations line item as the impact of the hedged transaction. For derivatives with fair value hedge accounting designation, we recognize gains or losses from the change in fair value of these derivatives, as well as the offsetting change in the fair value of the underlying hedged item, in earnings. Fair value gains and losses arising on derivative financial instruments not qualifying for hedge accounting are reported in our Consolidated Statement of Operations.
Financing Costs and Gain on Interest Rate Hedge	Financing costs and gain on interest rate hedge The interest rate in respect of the Senior Notes is fixed at 3.64% for the five year term of the agreement. The associated interest cost is recognized in interest expense in the period since drawdown in December 2015. Cash proceeds ( $4.6 million ) received in November 2015 in respect of the realized hedge gain are amortized to the Consolidated Statement of Operations, net against interest payable, over the period of the Senior Notes. Deferred financing costs (including issue costs relating to the Senior Notes) are reported at cost less accumulated amortization and the related amortization expense is included in interest expense, in our Consolidated Statement of Operations.
Reclassifications	Reclassifications Certain amounts in the consolidated financial statements have been reclassified where necessary to conform to the current year presentation.
Impact of New Accounting Pronouncements	Impact of new accounting pronouncements adopted during fiscal year ended December 31, 2019 Leases The Company adopted ASC 842 'Leases' (ASC 842) with a date of initial application of January 1, 2019. The lease accounting policy applied in preparation of the results for the twelve months ended December 31, 2019 therefore reflect application of ASC 842. ICON adopted the standard using the cumulative-effect adjustment approach. Under this transition method, ICON has applied the new standard as at the date of initial application (i.e. January 1, 2019), without restatement of comparative period amounts. The cumulative effect of applying the new standard is recorded as an adjustment to the opening Consolidated Balance Sheet as at the date of initial application (see note 28 - Impact of change in accounting policies ). The comparative information has not been adjusted and therefore the results for the years ended December 31, 2018 and December 31, 2017 continue to be reported under ASC 840 'Leases' (ASC 840). The new standard requires lessees to recognize the rights and obligations resulting from virtually all leases on the balance sheet as right-of-use (ROU) assets with corresponding lease liabilities. The most significant impact of application of the new standard for ICON relates to the recognition of ROU assets and lease liabilities on the Consolidated Balance Sheets for operating leases for certain property, vehicles and equipment. Prior to application of ASC 842, costs in respect of operating leases were charged to the Consolidated Statements of Operations on a straight-line basis over the lease term. A lease liability and ROU asset have been recorded on the Consolidated Balance Sheet as at January 1, 2019 of $106.5 million (see note 28 - Impact of change in accounting policies ). The net operating cost of leases recorded in the year ended December 31, 2019 is $33.0 million (see note 22 - Operating leases ). Pursuant to certain practical expedients available as part of adopting ASC 842, ICON has not reassessed; whether existing or expired contracts are or contain leases, the classification of existing or expired leases, or whether unamortized initial direct costs meet the new definition of initial direct costs under ASC 842. Additionally, ICON has elected to use hindsight in determining the lease term and in assessing impairment of ROU assets, if any. ICON determines if an arrangement is a lease at inception. Finance leases, if any, are depreciated on the same basis as property, plant and equipment. At December 31, 2019 and December 31, 2018 , the Group did not account for any leases as finance leases. Operating leases are included in operating ROU assets, other liabilities and non-current operating lease liabilities on our Consolidated Balance Sheets with the lease charge recognized on a straight-line basis over the lease term. ROU assets and lease liabilities are recognized based on the present value of future minimum lease payments over the lease term at commencement date or date of transition. Our lease terms may also include options to extend or terminate. ICON actively reviews options to extend or terminate leases and adjusts the ROU asset and lease liability when it is reasonably certain the option will be exercised. The ROU asset is adjusted for any prepayments made at the date of commencement and any initial direct costs incurred. As most of ICON's leases do not provide an implicit rate, the discount rate used is based on the rate of traded corporate bonds available at the commencement date adjusted for country risk, liquidity and lease term. Leasehold improvements are amortized over the shorter of the depreciable lives of the corresponding fixed assets or the lease term including any applicable renewals. Certain property leases include variable lease payments resulting from periodic rent increases based on an index which are recognized as incurred in the Consolidated Statements of Operations. ICON accounts for lease and non-lease components separately with lease components flowing through the Consolidated Balance Sheets and non-lease components expensed directly to the Consolidated Statements of Operations. Other We have reviewed the FASB issued Accounting Standards Update (ASU) accounting pronouncements and interpretations thereof that have effective dates during the periods reported. The following relevant ASUs have also been adopted in 2019: In August 2017, the FASB issued ASU 2017-12 'Derivatives and Hedging - Targeted Improvements to Accounting for Hedging Activities (Topic 815)' . The updated guidance expands an entity’s ability to hedge nonfinancial and financial risk components and reduce complexity in fair value hedges of interest rate risk. The guidance eliminates the requirement to separately measure and report hedge ineffectiveness and generally requires the entire change in the fair value of a hedging instrument to be presented in the same income statement line as the hedged item. The guidance also eases certain documentation and assessment requirements and modifies the accounting for components excluded from the assessment of hedge effectiveness. Entities will apply the amendments to cash flow and net investment hedge relationships that exist on the date of adoption using a modified retrospective approach. The presentation and disclosure requirements apply prospectively. This ASU was effective for public business entities, for annual and interim periods in fiscal years beginning after December 15, 2018. The adoption of this ASU did not have a significant impact on the financial statements. In July 2017, the FASB issued ASU 2017-11 'Earnings Per Share (Topic 260); Distinguishing Liabilities from Equity (Topic 480); Derivatives and Hedging (Topic 815): (Part I) Accounting for Certain Financial Instruments with Down Round Features, (Part II) Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception' under which down round features will not cause certain equity-linked financial instruments to be accounted for as derivatives. A company that presents EPS information will reflect the effect of a down round feature of free-standing equity-linked financial instruments in EPS only if it is triggered. The ASU was effective for public business entities, for annual and interim periods in fiscal years beginning after December 15, 2018. The adoption of this ASU did not impact on the financial statements. In January 2017, the FASB issued ASU 2017-04 'Intangibles - Goodwill and Other: Simplifying the test for goodwill impairment' which requires an entity to no longer perform a hypothetical purchase price allocation to measure goodwill impairment. Instead, impairment will be measured using the difference between the carrying amount and the fair value of the reporting unit. The ASU is effective for public businesses, that are SEC filers, for annual and interim periods in fiscal years beginning after December 15, 2019, with early adoption permitted. The Company early adopted this ASU from 1 January 2018. The adoption of this ASU did not have a significant impact on the financial statements. In July 2018, the FASB issued ASU 2018-09 'Codification Improvements' . This amendment makes changes to a variety of topics to clarify, correct errors in, or make minor improvements to the Accounting Standards Codification (ASC). The transition and effective date guidance is based on the facts and circumstances of each amendment. Some of the amendments do not require transition guidance and will be effective upon issuance of ASU 2018-09. The amendments effective upon issuance did not have a material impact on the Company's consolidated financial statements. A majority of the amendments do have transition guidance with effective dates for annual periods beginning after December 15, 2018. The adoption of this ASU did not have a significant impact on the financial statements. In June 2018, the FASB issued ASU 2018-07, which expands the scope of ASC 718 'Compensation—Stock Compensation' (ASC 718) to include share based payment transactions for acquiring goods and services from nonemployees and more closely aligns the accounting for employee and nonemployee share-based payments. This ASU was effective for public business entities for annual and interim periods in fiscal years beginning after December 15, 2018. The adoption of this ASU did not impact on the financial statements. In February 2018, the FASB issued ASU 2018-02, which allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act. This ASU was effective for all entities for annual and interim periods in fiscal years beginning after December 15, 2018. The adoption of this ASU did not have a significant impact on the financial statements. In February 2018, the FASB issued ASU 2018-03, which provided technical corrections and improvements to ASU No. 2016-01 'Financial Instruments—Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities' . The amendments clarify certain aspects of the guidance issued in update 2016-01. The ASU was effective for public business entities for fiscal years beginning after December 15, 2017. The adoption of this ASU did not have a significant impact on the financial statements. Impact of new accounting pronouncements which will be adopted during fiscal year ended December 31, 2020 In June 2016, the FASB issued ASU 2016-13 'Measurement of Credit Losses on Financial Instruments (Topic 326)' , which significantly changes the way entities recognize impairment of many financial assets by requiring immediate recognition of estimated credit losses expected to occur over their remaining life. The update provides guidance on the measurement of credit losses for most financial assets and certain other instruments that are not measured at fair value through net income. The amendment replaces the current incurred loss impairment approach with a methodology to reflect expected credit losses and requires consideration of a broader range of reasonable and supportable information to explain credit loss estimates. The updated guidance is to be applied on a modified retrospective approach and is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019 for public business entities that are SEC filers. The adoption of Topic 326 is not expected to have a significant impact on the financial statements. In August 2018, the FASB issued ASU No. 2018-15 'Intangibles - Goodwill and Other - Internal-Use Software: Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (Topic 350) '. The amendments in the update align the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). The ASU is effective for public businesses, that are SEC filers for fiscal years beginning after December 15, 2019, and for interim periods within those fiscal years and is to be applied either retrospectively or prospectively to all implementation costs incurred after the adoption date. The adoption of ASU 2018-15 is not expected to have a significant impact on the financial statements. In August 2018, the FASB issued ASU 2018-13 'Fair Value Measurement - Disclosure Framework (Topic 820)' . The updated guidance requires entities to disclose changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements and the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. Amendments in this guidance also require disclosure of transfers into and out of Level 3 of the fair value hierarchy, purchases and issues of Level 3 assets and liabilities, and clarify that the measurement uncertainty disclosure is about the uncertainty in measurement as of the reporting date. The guidance removes requirements to disclose the amounts and reasons for transfers between Level 1 and Level 2, policy for timing between of transfers between levels, and the valuation processes for Level 3 fair value measurements. The updated guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted for any removed or modified disclosures. The adoption of ASU 2018-13 is not expected to have a significant impact on the financial statements. In November 2019, the FASB issued ASU 2019-08 'Codification Improvements—Share-Based Consideration Payable to a Customer' . The amendments in this update require that an entity measure and classify share-based payment awards granted to a customer by applying the guidance in ASC 718. The amount recorded as a reduction of the transaction price is required to be measured on the basis of the grant-date fair value of the share-based payment award in accordance with ASC 718. The grant date is the date at which a grantor (supplier) and a grantee (customer) reach a mutual understanding of the key terms and conditions of a share-based payment award. The classification and subsequent measurement of the award are subject to the guidance in ASC 718 unless the share-based payment award is subsequently modified and the grantee is no longer a customer. The amendments in this update are effective for public business entities in fiscal years beginning after December 15, 2019. The adoption of ASU 2019-08 is not expected to have a significant impact on the financial statements. Impact of other new accounting pronouncements In August 2018, the FASB issued ASU 2018-14 'Compensation - Retirement Benefits - Defined Benefit Plans (Topic 715)'. The updated guidance requires additional disclosures of weighted-average interest crediting rates for cash balance plans and an explanation of the reasons for significant gains and losses related to changes in the benefit obligation. Amendments in the guidance also clarify the requirement to disclose the projected benefit obligation (PBO) and fair value of plan assets for plans with PBOs in excess of plan assets. The same disclosure is needed for the accumulated benefit obligation (ABO) and fair value of plan assets for plans with ABOs in excess of plan assets. The guidance removes certain previous disclosure requirements no longer considered cost beneficial. The amendments are effective for fiscal years ending after December 15, 2020, with early adoption permitted. The Company is currently assessing the impact of adopting the updated provisions. In December 2019, the FASB issued ASU 2019-12 'Simplifying the Accounting for Income Taxes (Topic 740)'. The amendments in this update simplify the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The amendments also improve consistent application of GAAP for other areas of Topic 740 by clarifying and amending existing guidance. The Company is currently assessing the impact of adopting the updated provisions. No other new accounting pronouncement issued or effective has had, or is expected to have, a material impact on the Company’s consolidated financial statements.

Significant Accounting Polici_3

Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Adjustments Resulting From Foreign Currency Translations	Amounts charged or credited to the Consolidated Statements of Operations for the years ended December 31, 2019 , December 31, 2018 and December 31, 2017 were as follows: Year ended December 31, 2019 2018 2017 (in thousands) Amounts charged/(credited) $ 590 $ (3,876 ) $ 7,760
Estimated Useful Lives of Assets	Depreciation of property, plant and equipment is computed using the straight line method based on the estimated useful lives of the assets as listed below: Years Building 40 Computer equipment and software 2-8 Office furniture and fixtures 8 Laboratory equipment 5 Motor vehicles 5

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Cost and Fair Value of Investments	December 31, 2019 December 31, 2018 (in thousands) Available for sale investments at start of year $59,910 $77,589 Purchases 9,603 80,956 Sales and maturities (21,686 ) (99,865 ) Interest on short term investments 1,065 1,329 Realized gain on sale of short term investments 55 56 Unrealized capital gain/(loss) – investments 681 (155 ) Available for sale investments at end of year $49,628 $59,910
Available For Sale Short Term Investments by Major Security Type	The following table represents our available for sale short term investments by major security type as of December 31, 2019 : Maturity by period Cost Total Unrealized gains / (losses) Fair Value Total Less than 1 year 1 to 5 years (U.S.$ in millions) US government debt securities 14.91 0.16 15.07 6.01 9.06 Corporate securities 32.57 0.08 32.65 29.64 3.01 Term deposits 1.91 — 1.91 0.68 1.23 Total (U.S.$ in millions) $49.39 $0.24 $49.63 $36.33 $13.30

Goodwill (Tables)

Goodwill (Tables)	12 Months Ended
	Dec. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	December 31, 2019 December 31, 2018 (in thousands) Opening goodwill $ 756,260 $ 769,058 Current year acquisitions 126,932 — Prior period acquisition (note 4 (d)) — 1,048 Foreign exchange movement (22 ) (13,846 ) Closing goodwill $ 883,170 $ 756,260
Summary of Estimates of Fair Values of Assets Acquired and Liabilities Assumed	The following table summarizes the Company’s fair values of the assets acquired and liabilities assumed: January, 25 2019 (in thousands) Cash & cash equivalent $ 686 Property, plant and equipment 1,697 Operating right of use assets 2,866 Goodwill * 22,430 Customer relationships * 10,708 Order backlog * 2,787 Accounts receivable 3,100 Unbilled revenue 2,421 Other receivables 43 Prepayments and other current assets 908 Deferred tax asset 1,568 Accounts payable (1,280 ) Unearned revenue (540 ) Other liabilities (1,232 ) Current lease liabilities (699 ) Non-current lease liabilities (2,167 ) Non-current other liabilities (1,123 ) Net assets acquired $ 42,173 Cash outflows $ 42,349 Working capital adjustment (176 ) Total consideration $ 42,173 *Goodwill represents the acquisition of an established workforce with experience in molecular diagnostic specialty laboratory services and commercialization of precision medicines in oncology. None of the goodwill recognized is expected to be deductible for income tax purposes. In finalizing the goodwill on acquisition of MMD in the twelve month period from acquisition, fair value adjustments were made which resulted in increases in unbilled revenue ( $2.1 million ), deferred tax asset ( $3.7 million ), accounts payable ( $0.6 million ) and other liabilities ( $0.1 million ) and decreases in property, plant and equipment ( $0.1 million ) and unearned revenue ( $0.9 million ). Customer relationship and order backlog assets were also finalized. May 23, 2019 (in thousands) Cash & cash equivalents $ 7,719 Property, plant and equipment 670 Operating right of use assets 1,558 Goodwill * 81,430 Customer relationships ** 3,887 Order backlog ** 171 Patient database ** 2,542 Accounts receivable 3,488 Unbilled revenue 4,272 Other receivables 819 Prepayments and other current assets 406 Accounts payable (5,484 ) Unearned revenue (5,796 ) Other liabilities (6,622 ) Current lease liabilities (430 ) Non-current lease liabilities (1,128 ) Non-current deferred tax liability (1,226 ) Net assets acquired $ 86,276 Cash outflows $ 54,123 Working capital adjustment receivable (439 ) Redeemable noncontrolling interest *** 32,592 Total consideration (including redeemable noncontrolling interest) $ 86,276 *Goodwill represents the acquisition of an established workforce and access to a broad site network in Europe and Africa. None of the goodwill recognized is expected to be deductible for income tax purposes. **The Company has made an estimate of separate intangible assets acquired, being customer relationships, order book assets and patient database. This assessment will be finalized within 12 months of the date of acquisition. The fair value of MeDiNova’s intangible assets has been measured provisionally, pending receipt of a final independent valuation. ***The fair value of the redeemable noncontrolling interest on May 23, 2019 was $32.6 million which was estimated by applying an income based approach. The valuation approach used was based on the future earnings of the Company times an appropriate earnings multiple. Redemption of the noncontrolling interest will be based on the Company's earnings to March 31, 2020. July 27, 2017 (in thousands) Cash $ 19,649 Property, plant and equipment 4,872 Goodwill* 130,270 Order backlog 13,012 Customer relationships 18,392 Accounts receivable 15,874 Unbilled revenue 6,984 Prepayments and other current assets 2,587 Other receivables 1,430 Income taxes receivable 4,262 Accounts payable (2,994 ) Payments on account (31,445 ) Other liabilities (24,952 ) Non-current other liabilities (1,061 ) Non-current deferred tax liability (11,104 ) Net assets acquired $ 145,776 Cash outflows $ 144,131 Working capital adjustment 1,645 Total consideration $ 145,776 *Goodwill represents the acquisition of an established workforce with experience in late phase commercialization, analytics, real world evidence generation and strategic regulatory services in clinical trial services for biologics, drugs and devices. Goodwill related to the business acquired is not tax deductible. In finalizing the goodwill on acquisition of Mapi in the twelve month period from acquisition, fair value adjustments were made which resulted in increases in other liabilities ( $3.9 million ), plant and equipment ( $1.7 million ) and accounts receivable ( $1.7 million ) and income taxes receivable ( $1.5 million ) and decreases in unbilled revenue ( $4.8 million ), prepayments and other current assets ( $1.9 million ) and other receivables ( $1.0 million ) and in payment on account ( $2.6 million ) and non-current deferred tax liability ( $9.1 million ). Customer relationship and order backlog assets were also finalized. September 24, 2019 (in thousands) Cash & cash equivalents $ 3,292 Property, plant and equipment 564 Operating right of use assets 820 Goodwill * 23,072 Customer relationships ** 7,975 Order backlog ** 2,140 Accounts receivable 3,579 Unbilled revenue 186 Prepayments and other current assets 181 Other receivables 6 Accounts payable (799 ) Unearned revenue (1,446 ) Other liabilities (933 ) Current lease liabilities (289 ) Non-current lease liabilities (531 ) Net assets acquired $ 37,817 Cash outflows $ 34,976 Contingent consideration payable 2,500 Working capital adjustment payable 341 Total consideration $ 37,817 *Goodwill represents the acquisition of an established workforce and the capability to provide at-home trial services and site support solutions. The full amount of the goodwill recognized is expected to be deductible for income tax purposes. **The Company has made an estimate of separate intangible assets acquired, being customer relationships and order book assets. The fair value of Symphony’s intangible assets has been measured provisionally, pending receipt of a final independent valuation. This assessment will be finalized within 12 months of the date of acquisition.
Summary of Proforma Effect in Net Revenue Net Income and Earnings Per Share	The proforma effect of the MMD acquisition if completed on January 1, 2018 would have resulted in revenue, net income and earnings per share for the fiscal years ending December 31, 2019 and December 31, 2018 as follows: Year Ended 2019 2018 (in thousands) Revenue $ 2,806,908 $ 2,612,346 Net income $ 373,930 $ 321,698 Basic earnings per share $ 6.85 $ 5.94 Diluted earnings per share $ 6.79 $ 5.87 The proforma effect of the Mapi acquisition if completed on January 1, 2016 would have resulted in net revenue, net income and earnings per share for the fiscal years ending December 31, 2017 and December 31, 2016 as follows: Year Ended 2017 2016 (in thousands) Net revenue $ 1,811,018 $ 1,750,643 Net income $ 284,903 $ 263,101 Basic earnings per share $ 5.26 $ 4.76 Diluted earnings per share $ 5.19 $ 4.66 Year Ended 2019 2018 (in thousands) Revenue $ 2,807,788 $ 2,599,091 Net income $ 375,979 $ 323,759 Basic earnings per share $ 6.89 $ 5.98 Diluted earnings per share $ 6.83 $ 5.91 Year Ended 2019 2018 (in thousands) Revenue $ 2,818,280 $ 2,609,233 Net income $ 376,636 $ 324,671 Basic earnings per share $ 6.90 $ 6.00 Diluted earnings per share $ 6.84 $ 5.93

Intangible Assets (Tables)

Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Intangible Assets	December 31, 2019 December 31, 2018 Cost (in thousands) Customer relationships $ 132,192 $ 109,622 Technology asset 11,169 11,169 Order backlog 36,318 31,220 Trade names/ brands 2,766 2,766 Volunteer list 1,325 1,325 Non-compete arrangements 489 489 Patient database 2,542 — Foreign exchange movement (5,728 ) (5,085 ) Total cost 181,073 151,506 Accumulated amortization (116,196 ) (100,249 ) Foreign exchange movement 3,017 2,798 Net book value $ 67,894 $ 54,055
Schedule of Future Intangible Asset Amortization Expense	Future intangible asset amortization expense for the years ended December 31, 2020 to December 31, 2024 is as follows: Year Ended December 31, 2019 (in thousands) 2020 $ 17,381 2021 13,711 2022 8,022 2023 6,176 2024 5,793 $ 51,083

Property, Plant and Equipment_2

Property, Plant and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Schedule of Property Plant and Equipment, Net	December 31, 2019 December 31, 2018 (in thousands) Cost Land $ 3,724 $ 3,476 Building 84,603 86,621 Computer equipment and software 434,445 399,192 Office furniture and fixtures 87,855 83,215 Laboratory equipment 40,495 36,092 Leasehold improvements 31,144 25,827 Motor vehicles 199 144 682,465 634,567 Less accumulated depreciation and asset write offs (517,378 ) (475,898 ) Property, plant and equipment (net) $ 165,087 $ 158,669

Other Liabilities (Tables)

Other Liabilities (Tables)	12 Months Ended
	Dec. 31, 2019
Other Liabilities Disclosure [Abstract]
Schedule of Other Liabilities	December 31, 2019 December 31, 2018 (in thousands) General trade and overhead liabilities* $ 174,131 $ 118,845 Personnel related liabilities 157,146 171,866 Operating lease liability (note 22) 28,320 — Facility related liabilities 11,138 14,012 Other liabilities 6,531 4,289 Restructuring and other items (note 14) 1,232 8,089 Short term government grants (note 11) 45 42 $ 378,543 $ 317,143 *includes amounts due to third parties in respect of accrued reimbursable expenses of $142.6 million at December 31, 2019 and $85.6 million

Non-Current Other Liabilities (

Non-Current Other Liabilities (Tables)	12 Months Ended
	Dec. 31, 2019
Payables and Accruals [Abstract]
Non-Current Other Liabilities	December 31, 2019 December 31, 2018 (in thousands) Other non-current liabilities $ 11,459 $ 10,126 Defined benefit pension obligations, net (note 9) 6,053 3,320 $ 17,512 $ 13,446

Employee Benefits (Tables)

Employee Benefits (Tables)	12 Months Ended
	Dec. 31, 2019
Retirement Benefits [Abstract]
Schedule of Pension Costs	The pension costs of this plan are presented in the following tables in accordance with the requirements of ASC 715-60 'Defined Benefit Plans – Other Postretirement' . Funded status December 31, 2019 December 31, 2018 (in thousands) Projected benefit obligation $ (7,047 ) $ (5,279 ) Fair value of plan assets 6,014 4,707 Funded status $ (1,033 ) $ (572 ) Non-current other liabilities (note 8) $ (1,033 ) $ (572 ) Change in benefit obligation December 31, 2019 December 31, 2018 (in thousands) Benefit obligation at beginning of year $ 5,279 $ 5,927 Service cost 115 138 Interest cost 40 47 Plan participants' contributions 67 83 Settlement — (409 ) Prior service cost — (8 ) Transferred (benefits paid)/balances (72 ) (77 ) Actuarial loss/(gain) 1,479 (372 ) Foreign currency exchange rate changes 139 (50 ) Benefit obligation at end of year $ 7,047 $ 5,279 Change in plan assets December 31, December 31, 2019 2018 (in thousands) Fair value of plan assets at beginning of year $ 4,707 $ 5,202 Expected return on plan assets 35 41 Actual return/(loss) on plan assets 1,114 (240 ) Scheme contributions 89 109 Plan participants' contributions 67 83 Transferred (benefits paid)/balances (72 ) (77 ) Settlement — (409 ) Foreign currency exchange rate changes 74 (2 ) Fair value of plan assets at end of year $ 6,014 $ 4,707 'Defined Benefit Plans – Other Postretirement' . The plan has been closed to new entrants with effect from July 1, 2003. Funded status December 31, 2019 December 31, 2018 (in thousands) Projected benefit obligation $ (37,036 ) $ (30,045 ) Fair value of plan assets 32,016 27,297 Funded status $ (5,020 ) $ (2,748 ) Non-current other liabilities (note 8) $ (5,020 ) $ (2,748 ) Change in benefit obligation December 31, 2019 December 31, 2018 (in thousands) Benefit obligation at beginning of year $ 30,045 $ 37,759 Service cost 107 124 Interest cost 867 895 Plan participants' contributions 24 24 Expenses — — Benefits paid (177 ) (3,049 ) Actuarial loss/(gain) 4,756 (3,844 ) Foreign currency exchange rate changes 1,414 (1,864 ) Benefit obligation at end of year $ 37,036 $ 30,045 Change in plan assets December 31, 2019 December 31, 2018 (in thousands) Fair value of plan assets at beginning of year $ 27,297 $ 32,423 Actual return/(loss) on plan assets 3,504 (584 ) Employer contributions 148 153 Plan participants' contributions 24 24 Benefits paid (177 ) (3,049 ) Foreign currency exchange rate changes 1,220 (1,670 ) Fair value of plan assets at end of year $ 32,016 $ 27,297
Schedule of Funded Status	Funded status December 31, 2019 December 31, 2018 (in thousands) Projected benefit obligation $ (7,047 ) $ (5,279 ) Fair value of plan assets 6,014 4,707 Funded status $ (1,033 ) $ (572 ) Non-current other liabilities (note 8) $ (1,033 ) $ (572 ) 'Defined Benefit Plans – Other Postretirement' . The plan has been closed to new entrants with effect from July 1, 2003. Funded status December 31, 2019 December 31, 2018 (in thousands) Projected benefit obligation $ (37,036 ) $ (30,045 ) Fair value of plan assets 32,016 27,297 Funded status $ (5,020 ) $ (2,748 ) Non-current other liabilities (note 8) $ (5,020 ) $ (2,748 )
Schedule of Components of Net Periodic Benefit Cost	December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Service cost $ 115 $ 138 $ 243 Interest cost 40 47 54 Expected return on plan assets (35 ) (41 ) (47 ) Amortization of net gain (93 ) (69 ) (43 ) Amortization of prior service credit (9 ) (8 ) (8 ) Settlement — (93 ) (214 ) Net periodic benefit cost/(credit) $ 18 $ (26 ) $ (15 ) The following amounts were recorded in the Consolidated Statement of Operations as components of the net periodic benefit cost: December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Service cost $ 107 $ 124 $ 112 Interest cost 867 895 929 Expected return on plan assets (574 ) (624 ) (586 ) Amortization of net loss 67 248 250 Expenses — — (8 ) Net periodic benefit cost $ 467 $ 643 $ 697
Summary of Assumptions Used in Calculating Net Periodic Benefit Cost	The following assumptions were used at the commencement of the year in determining the net periodic pension benefit cost for the years ended December 31, 2019 , December 31, 2018 and December 31, 2017 : December 31, 2019 December 31, 2018 December 31, 2017 Discount rate 2.9 % 2.5 % 2.7 % Rate of compensation increase 3.7 % 3.7 % 3.9 % Expected rate of return on plan assets 2.1 % 2.0 % 2.1 % Other comprehensive income December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Actuarial loss/(gain) - benefit obligation $ 4,756 $ (3,844 ) $ 658 Actuarial (gain)/loss – plan assets (2,930 ) 1,208 (393 ) Actuarial loss recognized in net periodic benefit cost (67 ) (248 ) (250 ) Total $ 1,759 $ (2,884 ) $ 15 The following assumptions were used at the commencement of the year in determining the net periodic pension benefit cost for the years ended December 31, 2019 , December 31, 2018 and December 31, 2017 : December 31, 2019 December 31, 2018 December 31, 2017 Discount rate 0.80 % 0.80 % 0.75 % Rate of compensation increase 2.00 % 2.00 % 2.00 % Expected rate of return on plan assets 0.80 % 0.80 % 0.75 % Other comprehensive income December 31, 2019 December 31, 2018 December 31, 2017 Actuarial loss/(gain) - benefit obligation $ 1,479 $ (372 ) $ (626 ) Actuarial (gain)/loss – plan assets (1,114 ) 240 296 Prior service credit recognized in net periodic benefit cost — 93 215 Actuarial gain recognized in net periodic benefit cost 93 69 43 Amortization of net prior service credit 9 8 8 Net prior service cost occurring during the year — (9 ) (1 ) Total $ 467 $ 29 $ (65 )
Summary of Amounts Recognized in Accumulated Other Comprehensive Income Which Have Not Yet Been Recognized as Components of Net Periodic Benefit Cost	Amounts recognized in accumulated other comprehensive income that have not yet been recognized as components of net periodic benefit cost are as follows: December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Net actuarial gain $ (787 ) $ (1,254 ) $ (1,283 ) Total $ (787 ) $ (1,254 ) $ (1,283 ) Amounts recognized in accumulated other comprehensive income that have not yet been recognized as components of net periodic benefit cost are as follows: December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Net actuarial loss $ 6,013 $ 4,254 $ 7,138 Total $ 6,013 $ 4,254 $ 7,138
Summary of Assumptions Used in Calculating Pension Benefit Obligations	The following assumptions were used in determining the benefit obligation at December 31, 2019 and December 31, 2018 : December 31, 2019 December 31, 2018 Discount rate 2.1 % 2.9 % Rate of compensation increase 3.3 % 3.7 % The following assumptions were used in determining the benefit obligation at December 31, 2019 and December 31, 2018 : December 31, 2019 December 31, 2018 Discount rate 0.30 % 0.80 % Rate of compensation increase 2.00 % 2.00 %
Summary of Expected Long Term Rates of Return on Different Asset Classes	The expected long term rates of return on different asset classes are as follows: Asset Category Expected long-term return per annum Corporate Bonds (including 50% high yield bonds) 3.4 % Equities 5.8 % Secured Loans and Multi Asset Credit 3.6 % Cash 2.1 %
Schedule of Underlying Asset Split of Fund	The underlying asset split of the fund is shown below. Asset Category December 31, 2019 December 31, 2018 Corporate Bonds (including 50% high yield bonds) 40 % 25 % Equities 21 % — % Secured Loans and Multi Asset Credit 39 % — % Gilts — % 71 % Cash — % 4 % 100 % 100 %
Schedule of Plan Asset Fair Value Measurements	Quoted Prices in Active Markets for Identical Assets Level 1 December 31, 2019 December 31, 2018 (in thousands) Cash $ 17 $ 1,029 Fixed Income Securities L&G Life GPBF All World Equity Index Fund 6,753 — L&G Life DC Active Corporate Bond 6,412 — Stone Harbor High Yield Bond Fund 6,292 — Investec Global Total Return Credit Fund 3,166 — Stone Harbor Multi Asset Credit Portfolio 3,151 — Barings European Loan Fund Buy & Hold 6,225 — Legal and General Active Corporate Bond – Over 10 Year — 6,688 Legal and General Gilt Funds — 7,136 Legal and General Index Linked Gilt Funds — 12,444 $ 32,016 $ 27,297
Schedule of Annual Benefit Payments which Reflect Expected Future Service	The following annual benefit payments, which reflect expected future service as appropriate, are expected to be paid. (in thousands) 2020 $ 280 2021 276 2022 270 2023 265 2024 259 Years 2025 - 2029 $ 1,184 The following annual benefit payments, which reflect expected future service as appropriate, are expected to be paid. (in thousands) 2020 $ 323 2021 398 2022 428 2023 419 2024 549 Years 2025 - 2029 $ 3,904

Equity Incentive Schemes and _2

Equity Incentive Schemes and Stock Compensation Charges (Tables)	12 Months Ended
	Dec. 31, 2019
Share-based Payment Arrangement [Abstract]
Schedule of Transactions for Company's Share Option Plans	The following table summarizes the transactions for the Company's share option plans for the years ended December 31, 2019 , December 31, 2018 and December 31, 2017 : Options Granted Under Plans Weighted Average Exercise Price Weighted Average Grant Date Fair Value Outstanding at December 31, 2016 1,466,444 $ 43.45 $ 13.94 Granted 219,113 $ 85.98 $ 25.06 Exercised (458,243 ) $ 30.35 $ 10.72 Canceled (55,921 ) $ 54.35 $ 16.76 Outstanding at December 31, 2017 1,171,393 $ 56.02 $ 17.15 Granted 167,557 $ 118.90 $ 36.84 Exercised (408,699 ) $ 41.12 $ 13.55 Canceled (9,505 ) $ 32.35 $ 11.39 Outstanding at December 31, 2018 920,746 $ 74.32 $ 22.39 Granted 97,112 $ 140.13 $ 43.43 Exercised (329,870 ) $ 65.54 $ 19.78 Canceled/expired (31,881 ) $ 88.12 $ 26.77 Outstanding at December 31, 2019 656,107 $ 87.80 $ 26.60 Vested and exercisable at December 31, 2019 298,077 $ 68.72 $ 20.99
Schedule of Non Vested Shares Outstanding	Non-vested shares outstanding as at December 31, 2019 are as follows: Options Outstanding Number of Shares Weighted Average Exercise Price Weighted Average Fair Value Non-vested outstanding at December 31, 2018 522,823 $ 88.18 $ 26.41 Granted 97,112 140.13 43.43 Vested (233,861 ) 84.91 25.68 Forfeited (28,044 ) 97.36 29.24 Non-vested outstanding at December 31, 2019 358,030 $ 103.68 $ 31.28
Summary of Information Concerning Outstanding and Exercisable Share Options	The following table summarizes information concerning outstanding and exercisable share options as of December 31, 2019 : Options Outstanding Options Exercisable Range Exercise Price Number of Shares Weighted Average Remaining Contractual Life Weighted Average Exercise Price Number of Shares Weighted Average Exercise Price $ 22.30 35,405 0.32 35,405 $ 23.66 31 0.57 31 $ 26.71 450 0.69 450 $ 32.37 18,313 1.33 18,313 $ 36.22 645 1.46 645 $ 37.90 920 1.93 920 $ 40.83 22,740 2.39 22,740 $ 47.03 2,757 2.17 2,757 $ 48.67 10,128 2.21 10,128 $ 65.60 34,342 4.38 14,646 $ 66.47 3,445 3.39 2,096 $ 68.39 61,847 3.18 38,351 $ 71.95 100,123 4.17 68,595 $ 83.47 89,308 5.17 16,578 $ 90.03 52,082 5.38 23,594 $ 115.11 87,636 6.17 6,868 $ 125.74 41,270 6.38 35,960 $ 137.47 8,378 7.38 — $ 140.38 86,287 7.17 — — $22.30 - $140.38 656,107 4.76 $ 87.80 298,077 $ 68.72
Summary of Weighted Average Fair Values and Assumptions Used	The weighted average fair values and assumptions were as follows: Year Ended December 31, 2019 December 31, 2018 December 31, 2017 Weighted average fair value $ 43.43 $ 36.84 $ 25.06 Assumptions: Expected volatility 30 % 30 % 29 % Dividend yield — % — % — % Risk-free interest rate 2.55 % 2.76 % 1.93 % Expected life 5.0 years 5.0 years 5.0 years
Summary of RSU and PSU Activity	The following table summarizes RSU and PSU activity for the year ended December 31, 2019 : PSU Outstanding Number of Shares PSU Weighted Average Grant Date Fair Value PSU Weighted Average Remaining Contractual Life RSU Outstanding Number of Shares RSU Weighted Average Grant Date Fair Value RSU Weighted Average Remaining Contractual Life Outstanding at December 31, 2018 251,053 $ 85.95 0.96 534,677 $ 89.50 1.22 Granted 60,182 $ 140.13 160,237 $ 138.33 Shares vested (118,611 ) $ 71.45 (238,960 ) $ 69.19 Forfeited (16,635 ) $ 91.94 (66,054 ) $ 107.03 Outstanding at December 31, 2019 175,989 $ 110.79 1.04 389,900 $ 119.07 1.43
Schedule of Non-cash Stock Compensation Expense	Non-cash stock compensation expense has been allocated as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Direct costs $ 14,777 $ 17,408 $ 18,020 Selling, general and administrative 12,042 14,186 12,553 Total compensation costs $ 26,819 $ 31,594 $ 30,573

Government Grants (Tables)

Government Grants (Tables)	12 Months Ended
	Dec. 31, 2019
Deferred Revenue Disclosure [Abstract]
Government Grant	December 31, 2019 December 31, 2018 (in thousands) Received $ 3,539 $ 3,539 Less accumulated amortization (2,836 ) (2,792 ) Foreign exchange translation adjustment 155 172 Total government grants 858 919 Less current portion (45 ) (42 ) Non-current government grants $ 813 $ 877

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Summary of Components of Income Before Provision for Income Taxes	The components of income before income tax expense are as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Ireland $ 323,726 $ 243,988 $ 218,306 United States 21,073 27,499 28,426 Other 82,190 93,127 81,325 Income before income tax expense $ 426,989 $ 364,614 $ 328,057
Summary of Components of Provision for Income Taxes	The components of income tax expense are as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Income tax expense: Current tax expense: Ireland $ 35,955 $ 28,042 $ 20,084 United States 5,073 2,885 5,792 Other 11,642 9,379 9,964 Total current tax expense 52,670 40,306 35,840 Deferred tax (benefit)/expense: Ireland 2,833 1,054 261 United States (3,502 ) 875 8,980 Other (868 ) (277 ) 1,488 Total deferred tax (benefit)/expense (1,537 ) 1,652 10,729 Income tax expense allocated to continuing operations 51,133 41,958 46,569 Impact on other comprehensive income of the income tax consequence of : Currency impact on long term funding 25 119 973 Fair value of cash flow hedge — (148 ) 148 Total $ 51,158 $ 41,929 $ 47,690
Schedule of Reconciliation of Consolidated Reported Provision for Income Taxes and Statutory Rate	The Company's consolidated reported income tax expense differed from the amount that would result from applying the Irish statutory rate as set forth below: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Taxes at Irish statutory rate of 12.5% (2018:12.5%; 2017:12.5%) $ 53,374 $ 45,577 $ 41,007 Foreign and other income taxed at higher rates 7,356 7,649 6,324 Research & development tax incentives (893 ) (1,243 ) (830 ) Movement in valuation allowance (10 ) 5,667 1,329 Effects of change in tax rates 359 (147 ) 925 (Decrease)/increase in unrecognized tax benefits (1,273 ) (5,423 ) 933 Impact of stock compensation (7,383 ) (8,301 ) (9,917 ) Impact of deemed repatriation under US Tax Reform — — 7,694 Other (397 ) (1,821 ) (896 ) Provision for income taxes $ 51,133 $ 41,958 $ 46,569
Schedule of Tax Effects of Temporary Differences that Give Rise to Significant Portions of Deferred Tax Assets and Deferred Tax Liabilities	The tax effects of temporary differences that give rise to significant portions of deferred tax assets and deferred tax liabilities are presented below: December 31, 2019 December 31, 2018 (in thousands) Deferred tax liabilities: Property, plant and equipment $ 1,102 $ 981 Right-of-use-asset 11,838 — Goodwill 27,590 25,149 Intangible assets 11,805 9,397 Other 6,284 5,703 Total deferred tax liabilities recognized 58,619 41,230 Deferred tax assets: Operating loss and tax credits carryforwards 37,865 29,995 Property, plant and equipment 5,257 4,893 Lease Liabilities 11,754 — Accrued expenses and payments on account 26,380 24,599 Stock compensation 5,009 6,490 Deferred compensation 2,744 2,197 Unearned revenue 3,933 5,681 Other 604 2 Total deferred tax assets 93,546 73,857 Valuation allowance for deferred tax assets (27,721 ) (27,263 ) Deferred tax assets recognized 65,825 46,594 Overall net deferred tax asset $ 7,206 $ 5,364
Schedule of Expected Expiry Dates of NOL's	The expected expiry dates of these US losses are as follows: Federal NOL's State NOL's (in thousands) 2022-2035 $ 18,866 $ 44,986 2037 1,921 — Indefinite 1,363 49 $ 22,150 $ 45,035
Schedule of Reconciliation of Beginning and Ending Amount of Total Unrecognized Tax Benefits	A reconciliation of the beginning and ending amount of total unrecognized tax benefits is as follows: December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Unrecognized tax benefits at start of year $ 21,433 $ 23,720 $ 26,620 Increase related to prior year tax positions — 2,084 — Decrease related to prior year tax positions — (2,915 ) (3,050 ) Increase related to current year tax positions 1,588 3,065 4,765 Settlements (347 ) (182 ) (2,523 ) Lapse of statute of limitations (2,518 ) (4,339 ) (2,092 ) Unrecognized tax benefits at end of year $ 20,156 $ 21,433 $ 23,720

Restructuring Charges (Tables)

Restructuring Charges (Tables)	12 Months Ended
	Dec. 31, 2019
Restructuring and Related Activities [Abstract]
Schedule of Restructuring Charges	Year Ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Restructuring charges $ — $ 12,490 $ 7,753 Net charge $ — $ 12,490 $ 7,753
Schedule of Restructuring Reserve by Type of Cost	Workforce reductions Onerous Lease Total (in thousands) Total provision recognized $ 9,684 $ 2,806 $ 12,490 Utilized (5,399 ) (672 ) $ (6,071 ) Provision at December 31, 2018 $ 4,285 $ 2,134 $ 6,419 Utilized (3,554 ) (1,228 ) (4,782 ) Provision at December 31, 2019 $ 731 $ 906 $ 1,637

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Commitments for Operating Leases with Non-cancelable Terms	Future minimum rental commitments for operating leases with non-cancelable terms in excess of one year as of December 31, 2018 were as follows: Minimum rental payments (in thousands) 2019 32,634 2020 26,839 2021 21,306 2022 15,781 2023 10,829 Thereafter 19,194 Total 126,583

Disaggregation of Revenue (Tabl

Disaggregation of Revenue (Tables)	12 Months Ended
	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Schedule of Disaggregation of Revenue	Revenue disaggregated by customer profile is as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Top client $ 350,287 $ 352,335 $ 503,875 Clients 2-5 704,963 671,723 505,818 Clients 6-10 347,832 385,741 348,841 Clients 11-25 529,713 461,351 421,759 Other 873,044 724,627 622,028 Total $2,805,839 $2,595,777 $2,402,321

Accounts Receivable, Unbilled_2

Accounts Receivable, Unbilled Revenue (Contract Assets) and Unearned Revenue Or Payments On Account (Contract Liabilities) (Tables)	12 Months Ended
	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Schedule of Contracts with Customers, Asset and Liabilities	Accounts receivable and unbilled revenue are as follows: December 31, 2019 December 31, 2018 (in thousands) Billed services (accounts receivable) $ 535,088 $ 423,680 Unbilled services (unbilled revenue) 422,769 362,926 Accounts receivable and unbilled revenue 957,857 786,606 Allowance for doubtful accounts (note 18) (7,380 ) (8,889 ) Accounts receivable and unbilled revenue, net $ 950,477 $ 777,717 Unbilled services and unearned revenue or payments on account (contract assets and liabilities) were as follows: (in thousands, except percentages) December 31, 2019 December 31, 2018 $ Change % Change Unbilled services (unbilled revenue) $ 422,769 $ 362,926 $ 59,843 16.5 % Unearned revenue (payments on account) (366,988 ) (274,468 ) (92,520 ) 33.7 % Net balance $ 55,781 $ 88,458 $ (32,677 ) 36.9 %

Provision for Doubtful Debts (T

Provision for Doubtful Debts (Tables)	12 Months Ended
	Dec. 31, 2019
Accounts Receivable, after Allowance for Credit Loss [Abstract]
Schedule of Provision for Doubtful Debts	The Company does business with most major international pharmaceutical companies. Provision for doubtful debts at December 31, 2019 and December 31, 2018 comprises: December 31, 2019 December 31, 2018 (in thousands) Opening provision $ 8,889 $ 8,930 Amounts used during the year — (995 ) Amounts provided during the year 1,691 3,083 Amounts released during the year (3,226 ) (2,355 ) Foreign exchange 26 226 Closing provision $ 7,380 $ 8,889

Business Segment and Geograph_2

Business Segment and Geographical Information (Tables)	12 Months Ended
	Dec. 31, 2019
Segment Reporting [Abstract]
Schedule of Distribution of Net Revenue by Geographical Area	The distribution of revenue by geographical area was as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 Restated* (in thousands) Ireland $ 1,252,834 $ 1,066,200 $ 944,130 Rest of Europe 388,916 379,883 355,552 U.S. 892,497 894,978 881,829 Other 271,592 254,716 220,810 Total $ 2,805,839 $ 2,595,777 $ 2,402,321 * 2017 restated to reflect gross revenue.
Schedule of Distribution of Income from Operations by Geographical Area	The distribution of income from operations, including restructuring and other items, by geographical area was as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Ireland $ 314,287 $ 257,089 $ 232,032 Rest of Europe 37,997 36,280 26,493 U.S. 60,272 58,561 58,322 Other 20,850 21,427 21,491 Total $ 433,406 $ 373,357 $ 338,338 c) The distribution of income from operations, excluding restructuring and other items, by geographical area was as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Ireland $ 314,287 $ 269,196 $ 240,115 Rest of Europe 37,997 36,904 26,351 U.S. 60,272 58,340 58,164 Other 20,850 21,407 21,461 Total $ 433,406 $ 385,847 $ 346,091
Schedule of Distribution of Long-lived Assets, Net, by Geographical Area	The distribution of long-lived assets (including right-of-use assets (year ended December 31, 2019 only)), net, by geographical area was as follows: December 31, 2019 December 31, 2018 (in thousands) Ireland $ 110,522 $ 106,206 Rest of Europe 41,970 9,807 U.S. 72,578 25,535 Other 44,994 17,121 Total $ 270,064 $ 158,669
Schedule of Distribution of Depreciation and Amortization by Geographical Area	The distribution of depreciation, amortization and reduction in carrying value of the right-of-use assets (year ended December 31, 2019 only) by geographical area was as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Ireland $ 30,635 $ 34,721 $ 26,277 Rest of Europe 14,370 5,331 6,857 U.S. 33,922 21,605 24,246 Other 12,995 4,259 3,917 Total $ 91,922 $ 65,916 $ 61,297
Schedule of Distribution of Total Assets by Geographical Area	The distribution of total assets by geographical area was as follows: Year Ended December 31, 2019 December 31, 2018 (in thousands) Ireland $ 1,323,181 $ 1,073,411 Rest of Europe 660,797 514,010 U.S. 755,271 646,512 Other 168,263 120,322 Total $ 2,907,512 $ 2,354,255
Schedule of Distribution of Capital Expenditures by Geographical Area	The distribution of capital expenditures (including right-of-use assets (year ended December 31, 2019 only)) by geographical area was as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Ireland $ 32,526 $ 30,942 $ 24,468 Rest of Europe 13,971 2,590 2,819 U.S. 18,638 9,311 11,027 Other 15,010 5,554 6,403 Total $ 80,145 $ 48,397 $ 44,717
Schedule of Company's Net Revenue for Major Clients	The following table sets forth the clients which represented 10% or more of the Company's revenue in each of the periods set out below. Year ended December 31, 2019 December 31, 2018 December 31, 2017 Client A 12 % 14 % 21 % Client B 10 % — % — %
Schedule of Distribution of Interest Income by Geographical Area	The distribution of interest income by geographical area was as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Ireland $ 3,674 $ 2,620 $ 1,084 Rest of Europe 2,242 1,750 1,222 U.S. 111 17 16 Other 832 372 24 Total $ 6,859 $ 4,759 $ 2,346
Schedule of Distribution of Tax Charge by Geographical Area	The distribution of the income tax charge by geographical area was as follows: Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Ireland $ 38,788 $ 29,096 $ 20,345 Rest of Europe 4,234 (434 ) 1,921 U.S. 1,571 3,761 14,772 Other 6,540 9,535 9,531 Total $ 51,133 $ 41,958 $ 46,569

Supplemental Disclosure of Ca_2

Supplemental Disclosure of Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2019
Supplemental Cash Flow Elements [Abstract]
Schedule of Supplemental Disclosure of Cash Flow Information	Year ended December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Cash paid for interest $ 13,059 $ 13,060 $ 13,094 Cash paid for income taxes (net of refunds) $ 29,836 $ 18,558 $ 12,305

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule of Accumulated Other Comprehensive Income	Year ended December 31, 2019 December 31, 2018 (in thousands) Currency translation adjustments $ (64,023 ) $ (62,710 ) Currency impact on long term funding (7,726 ) (5,016 ) Actuarial loss on defined benefit pension plan (note 9) (5,226 ) (3,000 ) Unrealized capital gain – investments (note 3) 231 (450 ) Realized gain on interest rate hedge 4,658 4,658 Amortization of interest rate hedge (3,733 ) (2,810 ) Total $ (75,819 ) $ (69,328 )

Operating Leases (Tables)

Operating Leases (Tables)	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Lease Cost	Lease costs recorded under operating leases for the year ended December 31, 2019 were as follows: Year ended December 31, 2019 Operating lease costs $ 34,759 Income from sub-leases (1,761 ) Net operating lease costs $ 32,998
Operating Lease Maturity	Future minimum lease payments under non-cancelable leases as of December 31, 2019 were as follows: Minimum rental payments (in thousands) 2020 $ 28,320 2021 25,315 2022 19,433 2023 14,053 2024 8,839 Thereafter 17,264 Total future minimum lease payments 113,224 Lease imputed interest (8,311 ) Total $ 104,913

Net Income Per Ordinary Share_2

Net Income Per Ordinary Share (Tables)	12 Months Ended
	Dec. 31, 2019
Earnings Per Share [Abstract]
Reconciliation of Number of Shares Used in Computation of Basic and Diluted Net Income Per Ordinary Share	The reconciliation of the number of shares used in the computation of basic and diluted net income per ordinary share is as follows: December 31, 2019 December 31, 2018 December 31, 2017 Weighted average number of ordinary shares outstanding for basic net income per ordinary share 53,859,537 54,118,764 54,129,439 Effect of dilutive share options outstanding 473,924 671,899 719,607 Weighted average number of ordinary shares outstanding for diluted net income per ordinary share 54,333,461 54,790,663 54,849,046
Reconciliation of Net Income Attributable to the Group Per the Statement of Operating Income and Net Income Used For Net Income Per Ordinary Share	The reconciliation between net income attributable to the Group per the Statement of Operating Income and the net income used to calculate net income per ordinary share attributable to the Group is as follows: December 31, 2019 December 31, 2018 December 31, 2017 (in thousands) Net income attributable to the Group $ 373,986 322,656 $ 281,488 Noncontrolling interest adjustment to redemption amount (5,048 ) — — Net income attributable to the Group (including NCI redemption adjustment) 368,938 322,656 281,488 December 31, 2019 December 31, 2018 December 31, 2017 Net income per Ordinary Share attributable to the Group (including NCI redemption adjustment): Basic $ 6.85 $ 5.96 $ 5.20 Diluted $ 6.79 $ 5.89 $ 5.13

Description of Business (Detail

Description of Business (Details)	12 Months Ended
	Dec. 31, 2019EmployeeCountryLocation
Product Information [Line Items]
Number of employees | Employee	14,650
Number of locations in which company operates | Location	97
Number of countries in which company operates | Country	40
Geographic Concentration Risk | United States | Net Revenue
Product Information [Line Items]
Percentage of company revenue	31.80%
Geographic Concentration Risk | Europe | Net Revenue
Product Information [Line Items]
Percentage of company revenue	58.50%
Geographic Concentration Risk | Rest of World | Net Revenue
Product Information [Line Items]
Percentage of company revenue	9.70%

Significant Accounting Polici_4

Significant Accounting Policies - Narrative (Details) - USD ($)	1 Months Ended		12 Months Ended
	Dec. 31, 2015	Nov. 30, 2015	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Commission costs				$ 12,000,000
Advertising and promotion costs			$ 8,088,451	6,516,637	$ 6,744,333
Current bank credit lines and loan facilities (Note 23)			349,640,000	0
Goodwill impairment charge			0	0	$ 0
Carrying value of inventory			$ 3,200,000	$ 2,300,000
Senior Notes
Debt Instrument [Line Items]
Current bank credit lines and loan facilities (Note 23)	$ 350,000,000
Debt instrument, interest rate	3.64%		3.64%
Debt instrument, term	5 years		5 years
Cash proceeds from interest rate hedge		$ 4,600,000

Significant Accounting Polici_5

Significant Accounting Policies - Adjustments Resulting from Foreign Currency Translation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Foreign Currency [Abstract]
Amounts charged/(credited)	$ 590	$ (3,876)	$ 7,760

Significant Accounting Polici_6

Significant Accounting Policies - Estimated Useful Lives of Assets (Details)	12 Months Ended
	Dec. 31, 2019
Building
Property, Plant and Equipment [Line Items]
Estimated useful lives	40 years
Computer equipment and software | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	2 years
Computer equipment and software | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	8 years
Office furniture and fixtures
Property, Plant and Equipment [Line Items]
Estimated useful lives	8 years
Laboratory equipment
Property, Plant and Equipment [Line Items]
Estimated useful lives	5 years
Motor vehicles
Property, Plant and Equipment [Line Items]
Estimated useful lives	5 years

Investments - Available For Sal

Investments - Available For Sale Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation Of Debt Securities, Available-For-Sale [Roll Forward]
Available for sale investments at start of year	$ 59,910	$ 77,589
Purchases	9,603	80,956	$ 41,701
Sales and maturities	(21,686)	(99,865)	(33,086)
Interest on short term investments	1,065	1,329	1,088
Realized gain on sale of short term investments	55	56	112
Unrealized capital gain/(loss) – investments	681	(155)	(272)
Available for sale investments at end of year	$ 49,628	$ 59,910	$ 77,589

Investments - Narrative (Detail

Investments - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended			24 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Short term investments average maturity period	7 months 24 days	1 year 2 months 19 days
Purchase of investments in equity - long term	$ 3,890	$ 6,163	$ 0	$ 10,100
Increase (decrease) in fair value of investments in equity	(800)	800
Carrying value of long-term investments in equity	10,053	$ 6,963		10,053
Commitment to acquire future long-term investments	$ 22,500			$ 22,500

Investments - Available For S_2

Investments - Available For Sale Short Term Investments by Major Security Type (Details) $ in Thousands	Dec. 31, 2019USD ($)
Debt Securities, Available-for-sale [Line Items]
Cost Total	$ 49,390
Unrealized gains / (losses)	240
Fair Value Total	49,630
Maturity by period, less than 1 year	36,330
Maturity by period, 1 to 5 years	13,300
US government debt securities
Debt Securities, Available-for-sale [Line Items]
Cost Total	14,910
Unrealized gains / (losses)	160
Fair Value Total	15,070
Maturity by period, less than 1 year	6,010
Maturity by period, 1 to 5 years	9,060
Corporate securities
Debt Securities, Available-for-sale [Line Items]
Cost Total	32,570
Unrealized gains / (losses)	80
Fair Value Total	32,650
Maturity by period, less than 1 year	29,640
Maturity by period, 1 to 5 years	3,010
Term deposits
Debt Securities, Available-for-sale [Line Items]
Cost Total	1,910
Unrealized gains / (losses)	0
Fair Value Total	1,910
Maturity by period, less than 1 year	680
Maturity by period, 1 to 5 years	$ 1,230

Goodwill - Schedule of Goodwill

Goodwill - Schedule of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Roll Forward]
Opening goodwill	$ 756,260	$ 769,058
Current year acquisitions	126,932	0
Prior period acquisition (note 4 (d))	0	1,048
Foreign exchange movement	(22)	(13,846)
Closing goodwill	$ 883,170	$ 756,260

Goodwill - Narrative (Details)

Goodwill - Narrative (Details) - USD ($)	Sep. 24, 2019	May 23, 2019	Jan. 25, 2019	Jul. 27, 2017	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill					$ 883,170,000	$ 883,170,000	$ 883,170,000	$ 756,260,000	$ 769,058,000
Symphony
Business Acquisition [Line Items]
Percentage of share capital acquired	100.00%
Goodwill	$ 23,072,000
Valuation of contingent consideration at acquisition	2,500,000
Revenue of acquiree since acquisition date					4,500,000
Net income of acquiree since acquisition date					1,000,000
Consideration transferred	$ 37,817,000
MeDiNova
Business Acquisition [Line Items]
Percentage of share capital acquired		60.00%
Goodwill		$ 81,430,000
Revenue of acquiree since acquisition date						6,500,000
Net income of acquiree since acquisition date						4,700,000
Consideration transferred		$ 86,276,000
MMD
Business Acquisition [Line Items]
Percentage of share capital acquired			100.00%
Goodwill			$ 22,430,000
Revenue of acquiree since acquisition date							17,900,000
Net income of acquiree since acquisition date							1,100,000
Consideration transferred			$ 42,173,000
Mapi Group
Business Acquisition [Line Items]
Goodwill				$ 130,270,000
Consideration transferred				$ 145,776,000
Minimum | Symphony
Business Acquisition [Line Items]
Valuation of contingent consideration at acquisition					0	0	0
Maximum | Symphony
Business Acquisition [Line Items]
Valuation of contingent consideration at acquisition					$ 2,500,000	$ 2,500,000	$ 2,500,000

Goodwill - Summary of Estimates

Goodwill - Summary of Estimates of Fair Values of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Sep. 24, 2019	May 23, 2019	Jan. 25, 2019	Jul. 27, 2017	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Jul. 27, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill					$ 883,170	$ 883,170	$ 756,260		$ 769,058
Cash outflows						$ 131,272	$ 1,645		$ 144,131
Symphony
Business Acquisition [Line Items]
Cash & cash equivalents	$ 3,292
Property, plant and equipment	564
Operating right of use assets	820
Goodwill	23,072
Accounts receivable	3,579
Unbilled revenue	186
Prepayments and other current assets	181
Other receivables	6
Accounts payable	(799)
Unearned revenue (Payments on account)	(1,446)
Other liabilities	(933)
Current lease liabilities	(289)
Non-current lease liabilities	(531)
Net assets acquired	37,817
Cash outflows	34,976
Contingent consideration payable	2,500
Working capital adjustment	341
Total consideration	37,817
MeDiNova
Business Acquisition [Line Items]
Cash & cash equivalents		$ 7,719
Property, plant and equipment		670
Operating right of use assets		1,558
Goodwill		81,430
Accounts receivable		3,488
Unbilled revenue		4,272
Prepayments and other current assets		406
Other receivables		819
Accounts payable		(5,484)
Unearned revenue (Payments on account)		(5,796)
Other liabilities		(6,622)
Current lease liabilities		(430)
Non-current lease liabilities		(1,128)
Non-current deferred tax liability		(1,226)
Net assets acquired		86,276
Cash outflows		54,123
Working capital adjustment		(439)
Redeemable noncontrolling interest		32,592
Total consideration		86,276
MMD
Business Acquisition [Line Items]
Cash & cash equivalents			$ 686
Property, plant and equipment			1,697
Operating right of use assets			2,866
Goodwill			22,430
Accounts receivable			3,100
Unbilled revenue			2,421
Prepayments and other current assets			908
Other receivables			43
Deferred tax asset			1,568
Accounts payable			(1,280)
Unearned revenue (Payments on account)			(540)
Other liabilities			(1,232)
Current lease liabilities			(699)
Non-current lease liabilities			(2,167)
Non-current other liabilities			(1,123)
Net assets acquired			42,173
Cash outflows			42,349
Working capital adjustment			(176)
Total consideration			42,173
Unbilled revenue adjustment					2,100
Deferred tax asset adjustment					3,700
Accounts payable adjustment					600
Other liabilities adjustment					100
Property, plant and equipment adjustment					(100)
Unearned revenue (Payments on account) adjustment					$ (900)
Mapi Group
Business Acquisition [Line Items]
Cash & cash equivalents				$ 19,649
Property, plant and equipment				4,872
Goodwill				130,270
Accounts receivable				15,874
Unbilled revenue				6,984
Prepayments and other current assets				2,587
Other receivables				1,430
Income taxes receivable				4,262
Accounts payable				(2,994)
Unearned revenue (Payments on account)				(31,445)
Other liabilities				(24,952)
Non-current other liabilities				(1,061)
Non-current deferred tax liability				(11,104)
Net assets acquired				145,776
Cash outflows				144,131
Working capital adjustment				1,645
Total consideration				145,776
Unbilled revenue adjustment								$ (4,800)
Other liabilities adjustment								3,900
Property, plant and equipment adjustment								1,700
Unearned revenue (Payments on account) adjustment								(2,600)
Accounts receivable adjustment								1,700
Income taxes receivable adjustment								1,500
Prepayments and other current assets adjustment								(1,900)
Other receivables adjustment								(1,000)
Non-current deferred tax liabilities adjustment								$ (9,100)
Customer relationships | Symphony
Business Acquisition [Line Items]
Intangible assets	7,975
Customer relationships | MeDiNova
Business Acquisition [Line Items]
Intangible assets		3,887
Customer relationships | MMD
Business Acquisition [Line Items]
Intangible assets			10,708
Customer relationships | Mapi Group
Business Acquisition [Line Items]
Intangible assets				18,392
Order backlog | Symphony
Business Acquisition [Line Items]
Intangible assets	$ 2,140
Order backlog | MeDiNova
Business Acquisition [Line Items]
Intangible assets		171
Order backlog | MMD
Business Acquisition [Line Items]
Intangible assets			$ 2,787
Order backlog | Mapi Group
Business Acquisition [Line Items]
Intangible assets				$ 13,012
Patient database | MeDiNova
Business Acquisition [Line Items]
Intangible assets		$ 2,542

Goodwill - Summary of Proforma

Goodwill - Summary of Proforma Effect in Net Revenue, Net Income and Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Symphony
Business Acquisition [Line Items]
Net revenue	$ 2,818,280	$ 2,609,233
Net income	$ 376,636	$ 324,671
Basic earnings per share (dollars per share)	$ 6.90	$ 6
Diluted earnings per share (dollars per share)	$ 6.84	$ 5.93
MeDiNova
Business Acquisition [Line Items]
Net revenue	$ 2,807,788	$ 2,599,091
Net income	$ 375,979	$ 323,759
Basic earnings per share (dollars per share)	$ 6.89	$ 5.98
Diluted earnings per share (dollars per share)	$ 6.83	$ 5.91
MMD
Business Acquisition [Line Items]
Net revenue	$ 2,806,908	$ 2,612,346
Net income	$ 373,930	$ 321,698
Basic earnings per share (dollars per share)	$ 6.85	$ 5.94
Diluted earnings per share (dollars per share)	$ 6.79	$ 5.87
Mapi Group
Business Acquisition [Line Items]
Net revenue			$ 1,811,018	$ 1,750,643
Net income			$ 284,903	$ 263,101
Basic earnings per share (dollars per share)			$ 5.26	$ 4.76
Diluted earnings per share (dollars per share)			$ 5.19	$ 4.66

Intangible Assets - Summary (De

Intangible Assets - Summary (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Cost
Total cost	$ 181,073	$ 151,506
Foreign exchange movement	(5,728)	(5,085)
Accumulated amortization	(116,196)	(100,249)
Foreign exchange movement	3,017	2,798
Net book value	67,894	54,055
Customer relationships
Cost
Total cost	132,192	109,622
Technology asset
Cost
Total cost	11,169	11,169
Order backlog
Cost
Total cost	36,318	31,220
Trade names/ brands
Cost
Total cost	2,766	2,766
Volunteer list
Cost
Total cost	1,325	1,325
Non-compete arrangements
Cost
Total cost	489	489
Patient database
Cost
Total cost	$ 2,542	$ 0

Intangible Assets - Narrative (

Intangible Assets - Narrative (Details) $ in Thousands

Sep. 24, 2019USD ($)

May 23, 2019USD ($)

Jan. 25, 2019USD ($)

Jul. 27, 2017USD ($)

Sep. 15, 2016USD ($)

Dec. 04, 2015USD ($)Site

Feb. 27, 2015USD ($)

May 07, 2014USD ($)

Feb. 28, 2012USD ($)

Feb. 15, 2012USD ($)

Jul. 14, 2011USD ($)

Dec. 31, 2019USD ($)

Dec. 31, 2018USD ($)

Indefinite-lived Intangible Assets [Line Items]

Amount amortized since date of acquisition

$ 116,196

$ 100,249

Symphony

Indefinite-lived Intangible Assets [Line Items]

Percentage of share capital acquired

100.00%

Amount amortized since date of acquisition

500

Symphony | Customer relationships

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 7,975

Amortization period

12 years

Symphony | Order backlog

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 2,140

Amortization period

2 years

MeDiNova

Indefinite-lived Intangible Assets [Line Items]

Percentage of share capital acquired

60.00%

Amount amortized since date of acquisition

500

MeDiNova | Customer relationships

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 3,887

Amortization period

12 years

MeDiNova | Patient database

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 2,542

Amortization period

7 years

MeDiNova | Order backlog

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 171

Amortization period

1 year

MMD

Indefinite-lived Intangible Assets [Line Items]

Percentage of share capital acquired

100.00%

Amount amortized since date of acquisition

1,900

MMD | Customer relationships

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 10,708

Amortization period

16 years

MMD | Order backlog

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 2,787

Amortization period

2 years

Mapi Group

Indefinite-lived Intangible Assets [Line Items]

Amount amortized since date of acquisition

9,500

Mapi Group | Customer relationships

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 18,392

Amortization period

8 years

Mapi Group | Order backlog

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 13,012

Amortization period

8 years 6 months

ICON Government & Public Health Solutions

Indefinite-lived Intangible Assets [Line Items]

Amount amortized since date of acquisition

5,000

ICON Government & Public Health Solutions | Customer relationships

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 4,000

Amortization period

7 years

ICON Government & Public Health Solutions | Order backlog

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 1,700

Amortization period

2 years

ICON Government & Public Health Solutions | Brand

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 1,400

Amortization period

5 years

PMG

Indefinite-lived Intangible Assets [Line Items]

Amount amortized since date of acquisition

7,000

Number of clinical research sites acquired | Site

52

PMG | Customer relationships

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 6,900

Amortization period

7 years

PMG | Order backlog

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 3,000

Amortization period

2 years

MediMedia Pharma Solutions

Indefinite-lived Intangible Assets [Line Items]

Amount amortized since date of acquisition

18,200

MediMedia Pharma Solutions | Customer relationships

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 22,800

Amortization period

7 years

MediMedia Pharma Solutions | Order backlog

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 2,500

Amortization period

1 year

Aptiv Solutions

Indefinite-lived Intangible Assets [Line Items]

Amount amortized since date of acquisition

25,200

Aptiv Solutions | Customer relationships

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 21,400

Amortization period

7 years

Aptiv Solutions | Order backlog

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 7,900

Amortization period

3 years

PriceSpective

Indefinite-lived Intangible Assets [Line Items]

Amount amortized since date of acquisition

8,800

PriceSpective | Customer relationships

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 10,200

Amortization period

10 years

PriceSpective | Order backlog

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 400

Amortization period

9 months 18 days

PriceSpective | Non-compete arrangements

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 400

Amortization period

3 years

BeijingWits Medical

Indefinite-lived Intangible Assets [Line Items]

Amount amortized since date of acquisition

1,800

BeijingWits Medical | Customer relationships

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 1,800

Amortization period

10 years

BeijingWits Medical | Order backlog

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 400

Amortization period

4 years

BeijingWits Medical | Non-compete arrangements

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 100

Amortization period

5 years

Firecrest Clinical Limited

Indefinite-lived Intangible Assets [Line Items]

Amount amortized since date of acquisition

$ 16,500

Firecrest Clinical Limited | Customer relationships

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 5,200

Amortization period

7 years 6 months

Firecrest Clinical Limited | Order backlog

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 1,200

Amortization period

1 year 2 months 12 days

Firecrest Clinical Limited | Technology asset

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 11,200

Amortization period

7 years 6 months

Firecrest Clinical Limited | Trade names acquired

Indefinite-lived Intangible Assets [Line Items]

Value of intangible assets acquired

$ 1,400

Amortization period

4 years 6 months

Intangible Assets - Future Inta

Intangible Assets - Future Intangible Asset Amortization Expense (Details) $ in Thousands	Dec. 31, 2019USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2020	$ 17,381
2021	13,711
2022	8,022
2023	6,176
2024	5,793
Finite Lived Intangible Assets, Amortization Expense, Net, Total	$ 51,083

Property, Plant and Equipment_3

Property, Plant and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Land	$ 3,724	$ 3,476
Building	84,603	86,621
Computer equipment and software	434,445	399,192
Office furniture and fixtures	87,855	83,215
Laboratory equipment	40,495	36,092
Leasehold improvements	31,144	25,827
Motor vehicles	199	144
Property, plant and equipment, gross	682,465	634,567
Less accumulated depreciation and asset write offs	(517,378)	(475,898)
Property, plant and equipment (net)	$ 165,087	$ 158,669

Other Liabilities (Details)

Other Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Other Liabilities Disclosure [Abstract]
General trade and overhead liabilities	$ 174,131	$ 118,845
Personnel related liabilities	157,146	171,866
Operating lease liability (note 22)	28,320
Facility related liabilities	11,138	14,012
Other liabilities	6,531	4,289
Restructuring and other items (note 14)	1,232	8,089
Short term government grants (note 11)	45	42
Other liabilities	378,543	317,143
Amounts due to third parties for reimbursable expenses	$ 142,600	$ 85,600

Non-Current Other Liabilities_2

Non-Current Other Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Payables and Accruals [Abstract]
Other non-current liabilities	$ 11,459	$ 10,126
Defined benefit pension obligations, net (note 9)	6,053	3,320
Non-current other liabilities	$ 17,512	$ 13,446

Employee Benefits - Narrative (

Employee Benefits - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	May 07, 2014
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Net gain (loss) for defined benefit pension plan that will be amortized from accumulated other comprehensive income into net periodic benefit cost over the next year	$ (200,000)
Net prior service cost (credit) for defined benefit pension plan that will be amortized from accumulated other comprehensive income into net periodic benefit cost over the next year	$ 0
Pension plan period	26 years
Expected long-term rate of return after application of a market value reduction factor (per annum)	4.00%
Contribution to pension fund in the year ending December 31, 2020	$ 200,000
Retirement period used as a basis to estimate expected cash flows	10 years
United Kingdom | World equities
Defined Benefit Plan Disclosure [Line Items]
Percentage of investments	20.00%
United Kingdom | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Percentage of investments	20.00%
United Kingdom | High yield bonds
Defined Benefit Plan Disclosure [Line Items]
Percentage of investments	20.00%
United Kingdom | Multi-asset credit fund
Defined Benefit Plan Disclosure [Line Items]
Percentage of investments	20.00%
United Kingdom | Senior secured loans
Defined Benefit Plan Disclosure [Line Items]
Percentage of investments	20.00%
Switzerland
Defined Benefit Plan Disclosure [Line Items]
Net gain (loss) for defined benefit pension plan that will be amortized from accumulated other comprehensive income into net periodic benefit cost over the next year	$ 6,000
Net prior service cost (credit) for defined benefit pension plan that will be amortized from accumulated other comprehensive income into net periodic benefit cost over the next year	(9,000)
Contribution to pension fund in the year ending December 31, 2020	$ 100,000
Retirement period used as a basis to estimate expected cash flows	10 years
Switzerland | Aptiv Solutions
Defined Benefit Plan Disclosure [Line Items]
Percentage of common stock acquired				100.00%
The Plan
Defined Benefit Plan Disclosure [Line Items]
Contributions percentage of annual compensation	8.00%
Employer contributions	$ 26,483,000	$ 25,241,000	$ 20,355,000
U.S. Plan
Defined Benefit Plan Disclosure [Line Items]
Contributions percentage of annual compensation	3.00%
Participant's contributions percentage matches	50.00%
Participant's contributions percentage of annual compensation	4.50%
Deferred salary arrangement employer contribution	$ 16,469,000	$ 15,532,000	$ 14,946,000

Employee Benefits - Funded Stat

Employee Benefits - Funded Status (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ (37,036)	$ (30,045)
Fair value of plan assets	32,016	27,297	$ 32,423
Funded status	(5,020)	(2,748)
Non-current other liabilities (note 8)	(5,020)	(2,748)
Switzerland
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	(7,047)	(5,279)
Fair value of plan assets	6,014	4,707	$ 5,202
Funded status	(1,033)	(572)
Non-current other liabilities (note 8)	$ (1,033)	$ (572)

Employee Benefits - Change in B

Employee Benefits - Change in Benefit Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
United Kingdom
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	$ 30,045	$ 37,759
Service cost	107	124	$ 112
Interest cost	867	895	929
Plan participants' contributions	24	24
Expenses	0	0	(8)
Benefits paid	(177)	(3,049)
Actuarial loss/(gain)	4,756	(3,844)
Foreign currency exchange rate changes	1,414	(1,864)
Benefit obligation at end of year	37,036	30,045	37,759
Switzerland
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	5,279	5,927
Service cost	115	138	243
Interest cost	40	47	54
Plan participants' contributions	67	83
Settlement	0	(409)
Prior service cost	0	(8)
Benefits paid	(72)	(77)
Actuarial loss/(gain)	1,479	(372)
Foreign currency exchange rate changes	139	(50)
Benefit obligation at end of year	$ 7,047	$ 5,279	$ 5,927

Employee Benefits - Change in P

Employee Benefits - Change in Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
United Kingdom
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	$ 27,297	$ 32,423
Expected return on plan assets	574	624	$ 586
Actual return/(loss) on plan assets	3,504	(584)
Employer contributions	148	153
Plan participants' contributions	24	24
Benefits paid	(177)	(3,049)
Foreign currency exchange rate changes	1,220	(1,670)
Fair value of plan assets at end of year	32,016	27,297	32,423
Switzerland
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	4,707	5,202
Expected return on plan assets	35	41	47
Actual return/(loss) on plan assets	1,114	(240)
Scheme contributions	89	109
Plan participants' contributions	67	83
Transferred (benefits paid)/balances	(72)	(77)
Settlement	0	(409)
Foreign currency exchange rate changes	74	(2)
Fair value of plan assets at end of year	$ 6,014	$ 4,707	$ 5,202

Employee Benefits - Components

Employee Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 107	$ 124	$ 112
Interest cost	867	895	929
Expected return on plan assets	(574)	(624)	(586)
Amortization of net gain	67	248	250
Expenses	0	0	(8)
Net periodic benefit cost	467	643	697
Switzerland
Defined Benefit Plan Disclosure [Line Items]
Service cost	115	138	243
Interest cost	40	47	54
Expected return on plan assets	(35)	(41)	(47)
Amortization of net gain	(93)	(69)	(43)
Amortization of prior service credit	(9)	(8)	(8)
Settlement	0	(93)	(214)
Net periodic benefit cost	$ 18	$ (26)	$ (15)

Employee Benefits - Net Periodi

Employee Benefits - Net Periodic Pension Benefit Cost Assumptions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.90%	2.50%	2.70%
Rate of compensation increase	3.70%	3.70%	3.90%
Expected rate of return on plan assets	2.10%	2.00%	2.10%
Other comprehensive income
Actuarial loss/(gain) - benefit obligation	$ 4,756	$ (3,844)	$ 658
Actuarial (gain)/loss – plan assets	(2,930)	1,208	(393)
Actuarial loss recognized in net periodic benefit cost	(67)	(248)	(250)
Total	$ 1,759	$ (2,884)	$ 15
Switzerland
Defined Benefit Plan Disclosure [Line Items]
Discount rate	0.80%	0.80%	0.75%
Rate of compensation increase	2.00%	2.00%	2.00%
Expected rate of return on plan assets	0.80%	0.80%	0.75%
Other comprehensive income
Actuarial loss/(gain) - benefit obligation	$ 1,479	$ (372)	$ (626)
Actuarial (gain)/loss – plan assets	(1,114)	240	296
Prior service credit recognized in net periodic benefit cost	0	93	215
Actuarial loss recognized in net periodic benefit cost	93	69	43
Amortization of net prior service credit	9	8	8
Net prior service cost occurring during the year	0	(9)	(1)
Total	$ 467	$ 29	$ (65)

Employee Benefits - Amounts Rec

Employee Benefits - Amounts Recognized in Accumulated Other Comprehensive Income not yet Recognized (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Total	$ 5,226	$ 3,000
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	6,013	4,254	$ 7,138
Total	6,013	4,254	7,138
Switzerland
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	(787)	(1,254)	(1,283)
Total	$ (787)	$ (1,254)	$ (1,283)

Employee Benefits - Assumptions

Employee Benefits - Assumptions Used in Determining Benefit Obligation (Details)	Dec. 31, 2019	Dec. 31, 2018
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.10%	2.90%
Rate of compensation increase	3.30%	3.70%
Switzerland
Defined Benefit Plan Disclosure [Line Items]
Discount rate	0.30%	0.80%
Rate of compensation increase	2.00%	2.00%

Employee Benefits - Expected Lo

Employee Benefits - Expected Long Term Rates of Return on Different Asset Classes (Details) - United Kingdom	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Expected long-term return per annum	2.10%	2.00%	2.10%
High yield percentage of corporate bond investment	50.00%
Corporate Bonds (including 50% high yield bonds)
Defined Benefit Plan Disclosure [Line Items]
Expected long-term return per annum	3.40%
Equities
Defined Benefit Plan Disclosure [Line Items]
Expected long-term return per annum	5.80%
Secured Loans and Multi Asset Credit
Defined Benefit Plan Disclosure [Line Items]
Expected long-term return per annum	3.60%
Cash
Defined Benefit Plan Disclosure [Line Items]
Expected long-term return per annum	2.10%

Employee Benefits - Actual Plan

Employee Benefits - Actual Plan Asset Allocation (Details) - United Kingdom	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Actual plan asset allocations	100.00%	100.00%
High yield percentage of corporate bond investment	50.00%
Corporate Bonds (including 50% high yield bonds)
Defined Benefit Plan Disclosure [Line Items]
Actual plan asset allocations	40.00%	25.00%
Equities
Defined Benefit Plan Disclosure [Line Items]
Actual plan asset allocations	21.00%	0.00%
Secured Loans and Multi Asset Credit
Defined Benefit Plan Disclosure [Line Items]
Actual plan asset allocations	39.00%	0.00%
Gilts
Defined Benefit Plan Disclosure [Line Items]
Actual plan asset allocations	0.00%	71.00%
Cash
Defined Benefit Plan Disclosure [Line Items]
Actual plan asset allocations	0.00%	4.00%

Employee Benefits - Plan Asset

Employee Benefits - Plan Asset Fair Value Measurements (Details) - United Kingdom - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 32,016	$ 27,297	$ 32,423
Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	32,016	27,297
Fair Value, Inputs, Level 1 | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17	1,029
Fair Value, Inputs, Level 1 | L&G Life GPBF All World Equity Index Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,753	0
Fair Value, Inputs, Level 1 | L&G Life DC Active Corporate Bond
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,412	0
Fair Value, Inputs, Level 1 | Stone Harbor High Yield Bond Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,292	0
Fair Value, Inputs, Level 1 | Investec Global Total Return Credit Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,166	0
Fair Value, Inputs, Level 1 | Stone Harbor Multi Asset Credit Portfolio
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,151	0
Fair Value, Inputs, Level 1 | Barings European Loan Fund Buy & Hold
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,225	0
Fair Value, Inputs, Level 1 | Legal and General Active Corporate Bond – Over 10 Year
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	6,688
Fair Value, Inputs, Level 1 | Legal and General Gilt Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	7,136
Fair Value, Inputs, Level 1 | Legal and General Index Linked Gilt Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 12,444

Employee Benefits - Annual Bene

Employee Benefits - Annual Benefit Payments (Details) $ in Thousands	Dec. 31, 2019USD ($)
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
2020	$ 323
2021	398
2022	428
2023	419
2024	549
Years 2025 - 2029	3,904
Switzerland
Defined Benefit Plan Disclosure [Line Items]
2020	280
2021	276
2022	270
2023	265
2024	259
Years 2025 - 2029	$ 1,184

Equity Incentive Schemes and _3

Equity Incentive Schemes and Stock Compensation Charges - Narrative (Details) - USD ($) $ in Thousands	Feb. 14, 2017	May 11, 2015	Jan. 17, 2003	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	May 16, 2019	Feb. 13, 2017
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Weighted average contractual term of options outstanding				4 years 9 months 3 days	5 years 3 days
Exercisable - weighted average remaining contractual life				3 years 7 months 20 days	3 years 9 months 29 days
Options expected to vest (in shares)				186,479	241,149
Intrinsic value of option exercised				$ 26,200
Intrinsic value of option outstanding				55,400
Intrinsic value of option exercisable				30,900
Total compensation costs				26,819	$ 31,594	$ 30,573
Non-cash stock compensation expense not yet recognized				$ 42,400
Unrecognized stock-based compensation expense, weighted average period (years)				2 years 2 months 4 days
Income tax benefit related to stock compensation				$ 8,200	12,700	9,300
Cash tax benefit related to stock options exercised				$ 1,900	3,600	$ 3,200
Consultants Stock Plan, 2008 Plan
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Ordinary shares which have been reserved for issuance (in shares)	1,000,000							400,000
Limit of shares issued or to be issued pursuant to options granted (in shares)	1,000,000
Employee Stock Plan, 2008 Plan
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Ordinary shares which have been reserved for issuance (in shares)	6,000,000
Maximum number of shares per employee (in shares)	400,000
Option Plans 2008 | Minimum
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Percentage of option price for fair value of ordinary share	100.00%
Employee Stock Plan, 2003 Plan
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Ordinary shares which have been reserved for issuance (in shares)			6,000,000
Maximum number of shares per employee (in shares)			400,000
Maximum number of award as percentage of shares outstanding			10.00%
Employee Stock Option
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Shares vesting period				5 years
Employee Stock Option | Vested and Unvested Options
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Options vesting percentage				20.00%
Restricted Stock Units 2013
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Ordinary shares which have been reserved for issuance (in shares)		4,100,000
Additional number of ordinary shares which have been reserved for issuance (in shares)		2,500,000
Consultants Restricted Stock Units 2019
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Ordinary shares which have been reserved for issuance (in shares)							250,000
Restricted Stock Units (RSUs)
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Fair value of stock units vested				$ 16,500	18,800
Performance Share Unit (PSUs)
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Fair value of stock units vested				$ 8,500	$ 14,700
PSUs Based on Service and EPS Targets | Maximum
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Stock units to be granted (in shares)				75,615
Award date, prior to 2018 | Employee Stock Option
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Shares vesting period				5 years
Shares expiration period				8 years
Award date, 2018 and thereafter | Employee Stock Option
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Shares vesting period				12 months
Shares expiration period				8 years
Non-executive director | Consultants Restricted Stock Units 2019
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Shares vesting period				12 months

Equity Incentive Schemes and _4

Equity Incentive Schemes and Stock Compensation Charges - Summary of Stock Option Activity (Details) - Stock Option And Award Plans - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Options Granted Under Plans
Beginning balance (in shares)	920,746	1,171,393	1,466,444
Granted (in shares)	97,112	167,557	219,113
Exercised (in shares)	(329,870)	(408,699)	(458,243)
Canceled/expired (in shares)	(31,881)	(9,505)	(55,921)
Ending balance (in shares)	656,107	920,746	1,171,393
Vested and exercisable at end of period (in shares)	298,077
Weighted Average Exercise Price
Beginning balance (usd per share)	$ 74.32	$ 56.02	$ 43.45
Granted (usd per share)	140.13	118.90	85.98
Exercised (usd per share)	65.54	41.12	30.35
Canceled/expired (usd per share)	88.12	32.35	54.35
Ending balance (usd per share)	87.80	74.32	56.02
Vested and exercisable at end of period (usd per share)	68.72
Weighted Average Grant Date Fair Value
Beginning balance (usd per share)	22.39	17.15	13.94
Granted (usd per share)	43.43	36.84	25.06
Exercised (usd per share)	19.78	13.55	10.72
Canceled/expired (usd per share)	26.77	11.39	16.76
Ending balance (usd per share)	26.60	$ 22.39	$ 17.15
Vested and exercisable at end of period (usd per share)	$ 20.99

Equity Incentive Schemes and _5

Equity Incentive Schemes and Stock Compensation Charges - Summary of Movement in Non-Vested Share Options (Details) - Employee Stock Option - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Options Outstanding Number of Shares
Beginning Balance (in shares)	522,823
Granted (in shares)	97,112
Vested (in shares)	(233,861)
Forfeited (in shares)	(28,044)
Ending Balance (in shares)	358,030	522,823
Weighted Average Exercise Price
Beginning balance (usd per share)	$ 88.18
Granted (usd per share)	140.13
Vested (usd per share)	84.91
Forfeited (usd per share)	97.36
Ending balance (usd per share)	103.68	$ 88.18
Weighted Average Fair Value
Beginning Balance (usd per share)	26.41
Granted (usd per share)	43.43	36.84	$ 25.06
Vested (usd per share)	25.68
Forfeited (usd per share)	29.24
Ending Balance (usd per share)	$ 31.28	$ 26.41

Equity Incentive Schemes and _6

Equity Incentive Schemes and Stock Compensation Charges - Outstanding and Exercisable Share Options (Details)	12 Months Ended
	Dec. 31, 2019$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share) | $ / shares	$ 140.38
Number of Shares (in shares)	656,107
Weighted Average Remaining Contractual Life	4 years 9 months 3 days
Weighted Average Exercise Price (usd per share) | $ / shares	$ 87.80
Number of Shares (in shares)	298,077
Weighted Average Exercise Price (usd per share) | $ / shares	$ 68.72
Minimum Range Exercise Price (usd per share) | $ / shares	22.30
Range 1
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share) | $ / shares	$ 22.30
Number of Shares (in shares)	35,405
Weighted Average Remaining Contractual Life	3 months 25 days
Number of Shares (in shares)	35,405
Range 2
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share) | $ / shares	$ 23.66
Number of Shares (in shares)	31
Weighted Average Remaining Contractual Life	6 months 25 days
Number of Shares (in shares)	31
Range 3
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share) | $ / shares	$ 26.71
Number of Shares (in shares)	450
Weighted Average Remaining Contractual Life	8 months 8 days
Number of Shares (in shares)	450
Range 4
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share) | $ / shares	$ 32.37
Number of Shares (in shares)	18,313
Weighted Average Remaining Contractual Life	1 year 3 months 29 days
Number of Shares (in shares)	18,313
Range 5
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share) | $ / shares	$ 36.22
Number of Shares (in shares)	645
Weighted Average Remaining Contractual Life	1 year 5 months 15 days
Number of Shares (in shares)	645
Range 6
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share) | $ / shares	$ 37.90
Number of Shares (in shares)	920
Weighted Average Remaining Contractual Life	1 year 11 months 4 days
Number of Shares (in shares)	920
Range 7
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share) | $ / shares	$ 40.83
Number of Shares (in shares)	22,740
Weighted Average Remaining Contractual Life	2 years 4 months 20 days
Number of Shares (in shares)	22,740
Range 8
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share) | $ / shares	$ 47.03
Number of Shares (in shares)	2,757
Weighted Average Remaining Contractual Life	2 years 2 months 1 day
Number of Shares (in shares)	2,757
Range 9
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share) | $ / shares	$ 48.67
Number of Shares (in shares)	10,128
Weighted Average Remaining Contractual Life	2 years 2 months 15 days
Number of Shares (in shares)	10,128
Range 10
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share) | $ / shares	$ 65.60
Number of Shares (in shares)	34,342
Weighted Average Remaining Contractual Life	4 years 4 months 17 days
Number of Shares (in shares)	14,646
Range 11
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share) | $ / shares	$ 66.47
Number of Shares (in shares)	3,445
Weighted Average Remaining Contractual Life	3 years 4 months 20 days
Number of Shares (in shares)	2,096
Range 12
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share) | $ / shares	$ 68.39
Number of Shares (in shares)	61,847
Weighted Average Remaining Contractual Life	3 years 2 months 4 days
Number of Shares (in shares)	38,351
Range 13
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share) | $ / shares	$ 71.95
Number of Shares (in shares)	100,123
Weighted Average Remaining Contractual Life	4 years 2 months 1 day
Number of Shares (in shares)	68,595
Range 14
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share) | $ / shares	$ 83.47
Number of Shares (in shares)	89,308
Weighted Average Remaining Contractual Life	5 years 2 months 1 day
Number of Shares (in shares)	16,578
Range 15
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share) | $ / shares	$ 90.03
Number of Shares (in shares)	52,082
Weighted Average Remaining Contractual Life	5 years 4 months 17 days
Number of Shares (in shares)	23,594
Range 16
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share) | $ / shares	$ 115.11
Number of Shares (in shares)	87,636
Weighted Average Remaining Contractual Life	6 years 2 months 1 day
Number of Shares (in shares)	6,868
Range 17
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share) | $ / shares	$ 125.74
Number of Shares (in shares)	41,270
Weighted Average Remaining Contractual Life	6 years 4 months 17 days
Number of Shares (in shares)	35,960
Range 18
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share) | $ / shares	$ 137.47
Number of Shares (in shares)	8,378
Weighted Average Remaining Contractual Life	7 years 4 months 17 days
Number of Shares (in shares)	0
Range 19
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share) | $ / shares	$ 140.38
Number of Shares (in shares)	86,287
Weighted Average Remaining Contractual Life	7 years 2 months 1 day
Number of Shares (in shares)	0

Equity Incentive Schemes and _7

Equity Incentive Schemes and Stock Compensation Charges - Schedule of Weighted Average Fair Values and Assumptions Used (Details) - Employee Stock Option - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value (usd per share)	$ 43.43	$ 36.84	$ 25.06
Assumptions:
Expected volatility	30.00%	30.00%	29.00%
Dividend yield	0.00%	0.00%	0.00%
Risk-free interest rate	2.55%	2.76%	1.93%
Expected life	5 years	5 years	5 years

Equity Incentive Schemes and _8

Equity Incentive Schemes and Stock Compensation Charges - Summary of RSU and PSU Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Performance Share Unit (PSUs)
Outstanding Number of Shares
Outstanding at beginning of period (in shares)	251,053
Granted (in shares)	60,182
Shares vested (in shares)	(118,611)
Forfeited (in shares)	(16,635)
Outstanding at ending of period (in shares)	175,989	251,053
Weighted Average Fair Value
Outstanding at beginning of period (usd per share)	$ 85.95
Granted (usd per share)	140.13
Shares vested (usd per share)	71.45
Forfeited (usd per share)	91.94
Outstanding at end of period (usd per share)	$ 110.79	$ 85.95
Weighted Average Remaining Contractual Life
Outstanding at end of period	1 year 14 days	29 days
Restricted Stock Units (RSUs)
Outstanding Number of Shares
Outstanding at beginning of period (in shares)	534,677
Granted (in shares)	160,237
Shares vested (in shares)	(238,960)
Forfeited (in shares)	(66,054)
Outstanding at ending of period (in shares)	389,900	534,677
Weighted Average Fair Value
Outstanding at beginning of period (usd per share)	$ 89.50
Granted (usd per share)	138.33
Shares vested (usd per share)	69.19
Forfeited (usd per share)	107.03
Outstanding at end of period (usd per share)	$ 119.07	$ 89.50
Weighted Average Remaining Contractual Life
Outstanding at end of period	1 year 5 months 4 days	1 year 2 months 19 days

Equity Incentive Schemes and _9

Equity Incentive Schemes and Stock Compensation Charges - Schedule of Non-cash Stock Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation costs	$ 26,819	$ 31,594	$ 30,573
Direct costs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation costs	14,777	17,408	18,020
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation costs	$ 12,042	$ 14,186	$ 12,553

Government Grants - Summary (De

Government Grants - Summary (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Received	$ 3,539	$ 3,539
Less accumulated amortization	(2,836)	(2,792)
Foreign exchange translation adjustment	155	172
Less current portion	(366,988)	(274,468)
Government Grants
Disaggregation of Revenue [Line Items]
Total government grants	858	919
Less current portion	(45)	(42)
Non-current government grants	$ 813	$ 877

Government Grants - Narrative (

Government Grants - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred Revenue Disclosure [Abstract]
Amortization of government grants	$ 44	$ 47	$ 44
Restricted retained earnings	$ 3,100	$ 3,200

Share Capital (Details)

Share Capital (Details) - USD ($)	Dec. 31, 2019	Jul. 22, 2016	Jul. 31, 2015	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2015	Jan. 08, 2019	Oct. 03, 2016
Equity, Class of Treasury Stock [Line Items]
Total proceeds from exercise of stock options by employees				$ 21,645,000	$ 16,842,000	$ 13,950,000
Ordinary shares redeemed, value				146,931,000	$ 128,960,000	$ 133,106,000
Buyback Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount			$ 400,000,000						$ 400,000,000
Ordinary shares redeemed (in shares)	35,100		5,316,062		4,026,576		6,198,481
Ordinary shares redeemed, value	$ 5,300,000		$ 400,000,000	$ 141,600,000	$ 372,100,000		$ 457,900,000
Number of shares authorized to be repurchased (in shares)								1,000,000
Employee Stock Option
Equity, Class of Treasury Stock [Line Items]
Options exercised by employees (in shares)				329,870	408,699	458,243
Average exercise price of option per share (usd per share)				$ 65.54	$ 41.12	$ 30.35
Total proceeds from exercise of stock options by employees				$ 21,600,000	$ 16,800,000	$ 13,900,000
Restricted Stock Units (RSUs)
Equity, Class of Treasury Stock [Line Items]
Ordinary shares issued in respect of certain RSUs previously awarded by the Company (in shares)				237,119	273,742	361,102
Performance Share Unit (PSUs)
Equity, Class of Treasury Stock [Line Items]
Ordinary shares issued in respect of certain PSUs previously awarded by the Company (in shares)				118,611	215,826	320,640
Maximum | Buyback Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized percentage		10.00%

Income Taxes - Components of In

Income Taxes - Components of Income Before Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Components of Income Before Income Tax Expense (Benefit) [Line Items]
Income before income tax expense	$ 426,989	$ 364,614	$ 328,057
Ireland
Schedule of Components of Income Before Income Tax Expense (Benefit) [Line Items]
Income before income tax expense	323,726	243,988	218,306
United States
Schedule of Components of Income Before Income Tax Expense (Benefit) [Line Items]
Income before income tax expense	21,073	27,499	28,426
Other
Schedule of Components of Income Before Income Tax Expense (Benefit) [Line Items]
Income before income tax expense	$ 82,190	$ 93,127	$ 81,325

Income Taxes - Components of Pr

Income Taxes - Components of Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current tax expense:
Current tax expense	$ 52,670	$ 40,306	$ 35,840
Deferred tax (benefit)/expense:
Deferred tax (benefit)/expense	(1,537)	1,652	10,729
Income tax expense allocated to continuing operations	51,133	41,958	46,569
Impact on other comprehensive income of the income tax consequence of :
Currency impact on long term funding	25	119	973
Fair value of cash flow hedge	0	(148)	148
Total	51,158	41,929	47,690
Ireland
Current tax expense:
Current tax expense	35,955	28,042	20,084
Deferred tax (benefit)/expense:
Deferred tax (benefit)/expense	2,833	1,054	261
Income tax expense allocated to continuing operations	38,788	29,096	20,345
United States
Current tax expense:
Current tax expense	5,073	2,885	5,792
Deferred tax (benefit)/expense:
Deferred tax (benefit)/expense	(3,502)	875	8,980
Income tax expense allocated to continuing operations	1,571	3,761	14,772
Other
Current tax expense:
Current tax expense	11,642	9,379	9,964
Deferred tax (benefit)/expense:
Deferred tax (benefit)/expense	$ (868)	$ (277)	$ 1,488

Income Taxes - Consolidated Rep

Income Taxes - Consolidated Reported Provision for Income Taxes Differed from Statutory Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Taxes at Irish statutory rate of 12.5% (2018:12.5%; 2017:12.5%)	$ 53,374	$ 45,577	$ 41,007
Foreign and other income taxed at higher rates	7,356	7,649	6,324
Research & development tax incentives	(893)	(1,243)	(830)
Movement in valuation allowance	(10)	5,667	1,329
Effects of change in tax rates	359	(147)	925
(Decrease)/increase in unrecognized tax benefits	(1,273)	(5,423)	933
Impact of stock compensation	(7,383)	(8,301)	(9,917)
Impact of deemed repatriation under US Tax Reform	0	0	7,694
Other	(397)	(1,821)	(896)
Income tax expense allocated to continuing operations	$ 51,133	$ 41,958	$ 46,569

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Impact of deemed repatriation under US Tax Reform	$ 0	$ 0	$ 7,694,000
Impact of tax rate change under US Tax Reform			500,000
Deferred tax asset in respect of operating leases	11,754,000
Deferred tax liability in respect of operating leases	11,838,000
Valuation allowance for deferred tax assets	27,721,000	27,263,000	22,400,000
Net change in the total valuation allowance	400,000	4,800,000
Tax credit carry forward, valuation allowance		6,200,000
Tax credit carryforward, valuation allowance release	3,400,000
Deferred tax liabilities, undistributed foreign earnings	5,400,000	4,900,000
Unrecognized tax benefit, potentially expire in 2019	3,800,000
Total unrecognized tax benefits net of potential benefits	20,200,000	21,400,000	23,700,000
Interest and penalties recognized as an expense	0	1,300,000	$ 900,000
Total accrued interest and penalties	1,100,000	1,100,000
Provision for income taxes
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Net change in the total valuation allowance	0	5,600,000
Other Comprehensive Income
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Net change in the total valuation allowance	400,000	$ 800,000
Foreign Country
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Ireland subsidiaries additional tax credit carryforward for income tax	6,500,000
Other non-U.S subsidiaries operating loss carryforwards for income tax	40,100,000
Other non-U.S subsidiaries tax credit carryforwards for income tax	5,100,000
Foreign Country | Tax Year 2020 to 2026
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Additional operating loss carryforward	16,200,000
Foreign Country | Tax Year 2027 to 2036
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Additional operating loss carryforward	19,100,000
United States
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
U.S. Federal net operating loss carry forwards currently available for offset	7,000,000
Alternative minimum tax credit carry forwards	300,000
Business credit carry forwards that are available to offset	1,000,000
United States | Federal NOL's
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Net operating loss carryforwards	22,150,000
U.S. federal net operating loss carry forwards	20,200,000
Tax credit carry forward	29,300,000
Other non-U.S subsidiaries operating loss carryforwards for income tax	1,363,000
United States | Tax Year 2020 to 2021 | Federal NOL's
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
U.S. federal net operating loss carry forwards	10,000,000
United States | Tax Year 2022 to 2026 | Federal NOL's
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
U.S. federal net operating loss carry forwards	9,800,000
United States | Tax Year 2027 to 2036 | Federal NOL's
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
U.S. federal net operating loss carry forwards	400,000
United States | State NOL's
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Net operating loss carryforwards	45,035,000
Other non-U.S subsidiaries operating loss carryforwards for income tax	$ 49,000

Income Taxes - Tax Effects of T

Income Taxes - Tax Effects of Temporary Differences That Give Rise to Significant Portions of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax liabilities:
Property, plant and equipment	$ 1,102	$ 981
Right-of-use-asset	11,838
Goodwill	27,590	25,149
Intangible assets	11,805	9,397
Other	6,284	5,703
Total deferred tax liabilities recognized	58,619	41,230
Deferred tax assets:
Operating loss and tax credits carryforwards	37,865	29,995
Property, plant and equipment	5,257	4,893
Lease Liabilities	11,754
Accrued expenses and payments on account	26,380	24,599
Stock compensation	5,009	6,490
Deferred compensation	2,744	2,197
Unearned revenue	3,933	5,681
Other	604	2
Total deferred tax assets	93,546	73,857
Valuation allowance for deferred tax assets	(27,721)	(27,263)	$ (22,400)
Deferred tax assets recognized	65,825	46,594
Overall net deferred tax asset	$ 7,206	$ 5,364

Income Taxes - Expected Expiry

Income Taxes - Expected Expiry Dates of NOL's (Details) - United States $ in Thousands	Dec. 31, 2019USD ($)
Federal NOL's
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, not subject to expiration	$ 1,363
Net operating loss carryforwards	22,150
Federal NOL's | 2022-2035
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, subject to expiration	18,866
Federal NOL's | 2037
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, subject to expiration	1,921
State NOL's
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, not subject to expiration	49
Net operating loss carryforwards	45,035
State NOL's | 2022-2035
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, subject to expiration	44,986
State NOL's | 2037
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, subject to expiration	$ 0

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Beginning and Ending Amount of Total Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits at start of year	$ 21,433	$ 23,720	$ 26,620
Increase related to prior year tax positions	0	2,084	0
Decrease related to prior year tax positions	0	(2,915)	(3,050)
Increase related to current year tax positions	1,588	3,065	4,765
Settlements	(347)	(182)	(2,523)
Lapse of statute of limitations	(2,518)	(4,339)	(2,092)
Unrecognized tax benefits at end of year	$ 20,156	$ 21,433	$ 23,720

Restructuring Charges - Recogni

Restructuring Charges - Recognized Restructuring (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restructuring and Related Activities [Abstract]
Restructuring charges	$ 0	$ 12,490,000	$ 7,753,000

Restructuring Charges - Narrati

Restructuring Charges - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 0	$ 12,490,000	$ 7,753,000
Restructuring reserve, current	1,200,000
Restructuring reserve, noncurrent	$ 400,000
Resource Rationalizations 2018
Restructuring Cost and Reserve [Line Items]
Restructuring charges		12,490,000
Resource Rationalizations 2018 | Workforce Reductions
Restructuring Cost and Reserve [Line Items]
Restructuring charges		9,684,000
Resource Rationalizations 2018 | Onerous Lease
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 2,806,000
Resource Rationalizations 2017
Restructuring Cost and Reserve [Line Items]
Restructuring charges			7,800,000
Resource Rationalizations 2017 | Workforce Reductions
Restructuring Cost and Reserve [Line Items]
Restructuring charges			$ 7,753,000

Restructuring Charges - Prior P

Restructuring Charges - Prior Period Restructuring Charges (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restructuring Reserve [Roll Forward]
Restructuring charges	$ 0	$ 12,490,000	$ 7,753,000
Resource Rationalizations 2018
Restructuring Reserve [Roll Forward]
Restructuring charges		12,490,000
Opening provision	6,419,000
Utilized	(4,782,000)	(6,071,000)
Closing provision	1,637,000	6,419,000
Resource Rationalizations 2018 | Workforce Reductions
Restructuring Reserve [Roll Forward]
Restructuring charges		9,684,000
Opening provision	4,285,000
Utilized	(3,554,000)	(5,399,000)
Closing provision	731,000	4,285,000
Resource Rationalizations 2018 | Onerous Lease
Restructuring Reserve [Roll Forward]
Restructuring charges		2,806,000
Opening provision	2,134,000
Utilized	(1,228,000)	(672,000)
Closing provision	906,000	2,134,000
Resource Rationalizations 2017
Restructuring Reserve [Roll Forward]
Restructuring charges			7,800,000
Resource Rationalizations 2017 | Workforce Reductions
Restructuring Reserve [Roll Forward]
Restructuring charges			7,753,000
Opening provision	2,082,000	3,097,000
Utilized	(2,082,000)	(1,015,000)	(4,656,000)
Closing provision	$ 0	$ 2,082,000	$ 3,097,000

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Non-cancelable operating leases for facilities expiration period			12 years
Operating leases rental expense	$ 40.3	$ 44

Commitments and Contingencies_2

Commitments and Contingencies - Future Minimum Rental Commitments for Operating Leases (Details) $ in Thousands	Dec. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
2019	$ 32,634
2020	26,839
2021	21,306
2022	15,781
2023	10,829
Thereafter	19,194
Total	$ 126,583

Disaggregation of Revenue (Deta

Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 2,805,839	$ 2,595,777	$ 1,758,439
Gross revenue	2,805,839	2,595,777	2,402,321
Top client
Disaggregation of Revenue [Line Items]
Revenue	350,287	352,335
Gross revenue			503,875
Clients 2-5
Disaggregation of Revenue [Line Items]
Revenue	704,963	671,723
Gross revenue			505,818
Clients 6-10
Disaggregation of Revenue [Line Items]
Revenue	347,832	385,741
Gross revenue			348,841
Clients 11-25
Disaggregation of Revenue [Line Items]
Revenue	529,713	461,351
Gross revenue			421,759
Other
Disaggregation of Revenue [Line Items]
Revenue	$ 873,044	$ 724,627
Gross revenue			$ 622,028

Accounts Receivable, Unbilled_3

Accounts Receivable, Unbilled Revenue (Contract Assets) and Unearned Revenue Or Payments On Account (Contract Liabilities) - Summary of Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
Billed services (accounts receivable)	$ 535,088	$ 423,680
Unbilled services (unbilled revenue)	422,769	362,926
Unbilled services (unbilled revenue)	957,857	786,606
Allowance for doubtful accounts (note 18)	(7,380)	(8,889)	$ (8,930)
Accounts receivable and unbilled revenue, net	950,477	777,717
Unearned revenue (payments on account)	(366,988)	(274,468)
Net balance	55,781	$ 88,458
Change in unbilled receivables	59,843
Change in unearned revenue (payments on account)	(92,520)
Change in advance payments netted against unbilled contracts receivable	$ (32,677)
Change in unbilled receivables, percent	16.50%
Change in unearned revenue (payments on account), percent	33.70%
Change in advance payments netted against unbilled contracts receivable, percent	36.90%

Accounts Receivable, Unbilled_4

Accounts Receivable, Unbilled Revenue (Contract Assets) and Unearned Revenue Or Payments On Account (Contract Liabilities) - Contracts Assets and Liabilities Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Amounts due to third parties for reimbursable expenses	$ 142,600	$ 85,600
Change in unbilled receivables	59,843
Change in unearned revenue (payments on account)	92,520
Change in advance payments netted against unbilled contracts receivable	(32,677)
Bad debt expense	$ 400

Accounts Receivable, Unbilled_5

Accounts Receivable, Unbilled Revenue (Contract Assets) and Unearned Revenue Or Payments On Account (Contract Liabilities) - Revenue Remaining Performance Obligations (Details) $ in Billions	Dec. 31, 2019USD ($)
Revenue from Contract with Customer [Abstract]
Revenue, remaining performance obligation, amount	$ 5.3
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, percent	48.00%
Revenue, remaining performance obligation, expected timing of satisfaction, period	12 months

Provision for Doubtful Debts (D

Provision for Doubtful Debts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Opening provision	$ 8,889	$ 8,930
Amounts used during the year	0	(995)
Amounts provided during the year	1,691	3,083
Amounts released during the year	(3,226)	(2,355)
Foreign exchange	26	226
Closing provision	$ 7,380	$ 8,889

Business Segment and Geograph_3

Business Segment and Geographical Information - Narrative (Details)	12 Months Ended
	Dec. 31, 2019segment
Segment Reporting [Abstract]
Number of operating segments	1

Business Segment and Geograph_4

Business Segment and Geographical Information - Distribution of Net Revenue by Geographical Area (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenue	$ 2,805,839	$ 2,595,777	$ 1,758,439
Gross revenue	2,805,839	2,595,777	2,402,321
Ireland
Segment Reporting Information [Line Items]
Revenue	1,252,834	1,066,200
Gross revenue			944,130
Rest of Europe
Segment Reporting Information [Line Items]
Revenue	388,916	379,883
Gross revenue			355,552
U.S.
Segment Reporting Information [Line Items]
Revenue	892,497	894,978
Gross revenue			881,829
Other
Segment Reporting Information [Line Items]
Revenue	$ 271,592	$ 254,716
Gross revenue			$ 220,810

Business Segment and Geograph_5

Business Segment and Geographical Information - Distribution of Income from Operations, Including Restructuring, by Geographical Area (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Income from operations	$ 433,406	$ 373,357	$ 338,338
Ireland
Segment Reporting Information [Line Items]
Income from operations	314,287	257,089	232,032
Rest of Europe
Segment Reporting Information [Line Items]
Income from operations	37,997	36,280	26,493
U.S.
Segment Reporting Information [Line Items]
Income from operations	60,272	58,561	58,322
Other
Segment Reporting Information [Line Items]
Income from operations	$ 20,850	$ 21,427	$ 21,491

Business Segment and Geograph_6

Business Segment and Geographical Information - Distribution of Income from Operations, Excluding Restructuring, by Geographical Area (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Income from operations, excluding restructuring and other items	$ 433,406	$ 385,847	$ 346,091
Ireland
Segment Reporting Information [Line Items]
Income from operations, excluding restructuring and other items	314,287	269,196	240,115
Rest of Europe
Segment Reporting Information [Line Items]
Income from operations, excluding restructuring and other items	37,997	36,904	26,351
U.S.
Segment Reporting Information [Line Items]
Income from operations, excluding restructuring and other items	60,272	58,340	58,164
Other
Segment Reporting Information [Line Items]
Income from operations, excluding restructuring and other items	$ 20,850	$ 21,407	$ 21,461

Business Segment and Geograph_7

Business Segment and Geographical Information - Distribution of Long-lived Assets, Net, by Geographical Area (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Long-lived assets	$ 270,064	$ 158,669
Ireland
Segment Reporting Information [Line Items]
Long-lived assets	110,522	106,206
Rest of Europe
Segment Reporting Information [Line Items]
Long-lived assets	41,970	9,807
U.S.
Segment Reporting Information [Line Items]
Long-lived assets	72,578	25,535
Other
Segment Reporting Information [Line Items]
Long-lived assets	$ 44,994	$ 17,121

Business Segment and Geograph_8

Business Segment and Geographical Information - Distribution of Depreciation and Amortization by Geographical Area (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Depreciation amortization and right-of-use assets amortization	$ 91,922
Depreciation and amortization	61,550	$ 65,916	$ 61,297
Ireland
Segment Reporting Information [Line Items]
Depreciation amortization and right-of-use assets amortization	30,635
Depreciation and amortization		34,721	26,277
Rest of Europe
Segment Reporting Information [Line Items]
Depreciation amortization and right-of-use assets amortization	14,370
Depreciation and amortization		5,331	6,857
U.S.
Segment Reporting Information [Line Items]
Depreciation amortization and right-of-use assets amortization	33,922
Depreciation and amortization		21,605	24,246
Other
Segment Reporting Information [Line Items]
Depreciation amortization and right-of-use assets amortization	$ 12,995
Depreciation and amortization		$ 4,259	$ 3,917

Business Segment and Geograph_9

Business Segment and Geographical Information - Distribution of Total Assets by Geographical Area (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Assets	$ 2,907,512	$ 2,354,255
Ireland
Segment Reporting Information [Line Items]
Assets	1,323,181	1,073,411
Rest of Europe
Segment Reporting Information [Line Items]
Assets	660,797	514,010
U.S.
Segment Reporting Information [Line Items]
Assets	755,271	646,512
Other
Segment Reporting Information [Line Items]
Assets	$ 168,263	$ 120,322

Business Segment and Geograp_10

Business Segment and Geographical Information - Distribution of Capital Expenditure by Geographical Area (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Capital expenditures	$ 80,145	$ 48,397	$ 44,717
Ireland
Segment Reporting Information [Line Items]
Capital expenditures	32,526	30,942	24,468
Rest of Europe
Segment Reporting Information [Line Items]
Capital expenditures	13,971	2,590	2,819
U.S.
Segment Reporting Information [Line Items]
Capital expenditures	18,638	9,311	11,027
Other
Segment Reporting Information [Line Items]
Capital expenditures	$ 15,010	$ 5,554	$ 6,403

Business Segment and Geograp_11

Business Segment and Geographical Information - Company's Net Revenue for Major Clients (Details) - Customer Concentration Risk - Net Revenue	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Client A
Revenue, Major Customer [Line Items]
Clients which represented 10% or more of the company's net revenue	12.00%	14.00%	21.00%
Client B
Revenue, Major Customer [Line Items]
Clients which represented 10% or more of the company's net revenue	10.00%	0.00%	0.00%

Business Segment and Geograp_12

Business Segment and Geographical Information - Distribution of Interest Income by Geographical Area (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Interest income	$ 6,859	$ 4,759	$ 2,346
Ireland
Segment Reporting Information [Line Items]
Interest income	3,674	2,620	1,084
Rest of Europe
Segment Reporting Information [Line Items]
Interest income	2,242	1,750	1,222
U.S.
Segment Reporting Information [Line Items]
Interest income	111	17	16
Other
Segment Reporting Information [Line Items]
Interest income	$ 832	$ 372	$ 24

Business Segment and Geograp_13

Business Segment and Geographical Information - Distribution of Income Tax Charge by Geographical Area (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Income tax charge	$ 51,133	$ 41,958	$ 46,569
Ireland
Segment Reporting Information [Line Items]
Income tax charge	38,788	29,096	20,345
Rest of Europe
Segment Reporting Information [Line Items]
Income tax charge	4,234	(434)	1,921
U.S.
Segment Reporting Information [Line Items]
Income tax charge	1,571	3,761	14,772
Other
Segment Reporting Information [Line Items]
Income tax charge	$ 6,540	$ 9,535	$ 9,531

Supplemental Disclosure of Ca_3

Supplemental Disclosure of Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Supplemental Cash Flow Elements [Abstract]
Cash paid for interest	$ 13,059	$ 13,060	$ 13,094
Cash paid for income taxes (net of refunds)	$ 29,836	$ 18,558	$ 12,305

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Currency translation adjustments	$ (64,023)	$ (62,710)
Currency impact on long term funding	(7,726)	(5,016)
Actuarial loss on defined benefit pension plan (note 9)	(5,226)	(3,000)
Unrealized capital gain – investments (note 3)	231	(450)
Total	(75,819)	(69,328)
Interest Rate Contract
Accumulated Other Comprehensive Income (Loss) [Line Items]
Realized gain on interest rate hedge	4,658	4,658
Amortization of interest rate hedge	$ (3,733)	$ (2,810)

Operating Leases - Lease Costs

Operating Leases - Lease Costs (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Leases [Abstract]
Operating lease costs	$ 34,759
Income from sub-leases	(1,761)
Net operating lease costs	$ 32,998

Operating Leases Operating Leas

Operating Leases Operating Leases - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net operating lease costs	$ 32,998,000
Costs related to variable lease payments	0
Operating lease right-of-use assets	104,977,000
Operating lease liabilities	104,913,000
Right-of-use assets obtained in exchange for lease obligations	$ 29,500,000
Weighted average remaining lease term (in years)	5 years 2 months 8 days
Weighted average discount rate	2.91%
Operating lease liabilities	$ 28,320,000
Selling, general and administrative
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net operating lease costs	30,500,000
Direct costs
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net operating lease costs	2,500,000
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets		$ 106,500,000
Operating lease liabilities		$ 106,500,000
Other current liabilities
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease liabilities	$ 28,300,000

Operating Leases Operating Le_2

Operating Leases Operating Leases - Operating Lease Maturity (Details) $ in Thousands	Dec. 31, 2019USD ($)
Leases [Abstract]
2020	$ 28,320
2021	25,315
2022	19,433
2023	14,053
2024	8,839
Thereafter	17,264
Total future minimum lease payments	113,224
Lease imputed interest	(8,311)
Total	$ 104,913

Debt - Senior Notes (Details)

Debt - Senior Notes (Details) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	Dec. 31, 2015	Nov. 30, 2015	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Short-term debt			$ 349,640	$ 0
Cash and short-term investments			$ 569,900
Senior Notes
Debt Instrument [Line Items]
Short-term debt	$ 350,000
Stated interest rate	3.64%		3.64%
Debt instrument, term	5 years		5 years
Cash proceeds from interest rate hedge		$ 4,600

Impact of New Accounting Pron_2

Impact of New Accounting Pronouncements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease liabilities	$ 104,913
Operating lease right-of-use assets	104,977
Net operating cost	$ 32,998
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease liabilities		$ 106,500
Operating lease right-of-use assets		$ 106,500

Related Parties (Details)

Related Parties (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Nov. 01, 2017
Subsidiaries | DS Biopharma Limited
Related Party Transaction [Line Items]
Revenue earned from related parties	$ 95,000	$ 633,000
Amounts due from related parties	36,000	338,000
Mr. Ciaran Murray
Related Party Transaction [Line Items]
Expenses incurred from related party transactions			$ 178,000
Fair value of asset transferred to related party				$ 77,000
Mr. Thomas Lynch
Related Party Transaction [Line Items]
Related party transaction amounts	151,360	274,519
Amounts due to related parties	$ 0	$ 64,000

Net Income Per Ordinary Share -

Net Income Per Ordinary Share - Reconciliation of Number of Shares Used in Computation of Basic and Diluted Net Income Per Ordinary Share (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Weighted average number of ordinary shares outstanding for basic net income per ordinary share (in shares)	53,859,537	54,118,764	54,129,439
Effect of dilutive share options outstanding (in shares)	473,924	671,899	719,607
Weighted average number of ordinary shares outstanding for diluted net income per ordinary share (in shares)	54,333,461	54,790,663	54,849,046

Net Income Per Ordinary Share_3

Net Income Per Ordinary Share - Reconciliation of Net Income Attributable to the Group Per the Statement of Operating Income and Net Income Used For Net Income Per Ordinary Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Net income attributable to the Group	$ 373,986	$ 322,656	$ 281,488
Noncontrolling interest adjustment to redemption amount	(5,048)	0	0
Net income attributable to the Group (including NCI redemption adjustment)	$ 368,938	$ 322,656	$ 281,488
Net income per Ordinary Share attributable to the Group (including NCI redemption adjustment):
Basic (dollars per share)	$ 6.85	$ 5.96	$ 5.20
Diluted (dollars per share)	$ 6.79	$ 5.89	$ 5.13

Subsequent Events (Details)

Subsequent Events (Details) - USD ($) $ in Millions	Jan. 22, 2020	Jan. 14, 2020	Jan. 08, 2019
Buyback Program
Subsequent Event [Line Items]
Number of shares authorized to be repurchased (in shares)			1,000,000
Subsequent Event | Buyback Program
Subsequent Event [Line Items]
Number of shares authorized to be repurchased (in shares)		1,000,000
Subsequent Event | Medpass Group Limited
Subsequent Event [Line Items]
Percentage of share capital acquired	100.00%
Consideration transferred	$ 39.2
Net assets acquired	$ 9.2

Impact of Change in Accountin_2

Impact of Change in Accounting Policies (Details) - USD ($)	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease liabilities	$ 104,913,000
Operating lease right-of-use assets	104,977,000
Shareholders' equity	1,618,055,000		$ 1,354,281,000	$ 1,142,896,000	$ 1,191,000,000	$ 945,174,000
Commission costs			12,000,000
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease liabilities		$ 106,500,000
Operating lease right-of-use assets		106,500,000
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Shareholders' equity	$ 1,110,226,000		$ 888,326,000	$ 694,696,000	$ 742,800,000	$ 587,847,000
Retained Earnings | Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Shareholders' equity		$ 0

Uncategorized Items - iconplc20

Label	Element	Value
Additional Paid-in Capital [Member]
Stockholders' Equity Attributable to Parent	us-gaap_StockholdersEquity	$ 481,337,000
AOCI Attributable to Parent [Member]
Stockholders' Equity Attributable to Parent	us-gaap_StockholdersEquity	(38,713,000)
Common Stock [Member]
Stockholders' Equity Attributable to Parent	us-gaap_StockholdersEquity	$ 4,664,000
Common Stock, Shares, Issued	us-gaap_CommonStockSharesIssued	54,081,601
Other Undenominated Capital [Member]
Stockholders' Equity Attributable to Parent	us-gaap_StockholdersEquity	$ 912,000
Redeemable Noncontrolling Interest [Member]
Redeemable Noncontrolling Interest, Equity, Carrying Amount	us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount	0
Accounting Standards Update 2016-09 [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	6,677,000
Accounting Standards Update 2016-09 [Member] | Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	6,677,000
Accounting Standards Update 2014-09 [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	(48,104,000)
Accounting Standards Update 2014-09 [Member] | Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ (48,104,000)