Related Party Transactions - Additional Information (Details)		3 Months Ended	6 Months Ended	12 Months Ended
	Jan. 11, 2017 USD ($)	Sep. 30, 2018 Director	Jun. 30, 2017 USD ($)	Dec. 31, 2018 USD ($) Agreement RenewalOption Building	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) Parcel	Dec. 31, 2011 Agreement RenewalOption	Dec. 31, 2012 USD ($)
Related Party Transaction [Line Items]
Accounts receivable and unbilled, net				$ 3,800,000	$ 1,000,000.0
Advanced billings				$ 400,000	1,700,000
Pre-funded study costs with related parties					1,000,000.0
Number of lease renewal, 10-year option | RenewalOption							1
Lease expiration year							2027
Number of lease agreements | Agreement							2
Lease occupancy year							2012
Lease term upon renewal							10 years
Term of lease				15 years
Deemed landlord liability, long-term portions				$ 24,484,000	26,602,000
Accounts payable includes related parties				300,000	200,000
Cinven
Related Party Transaction [Line Items]
Members of board of directors resigned as result of remaining shares of common stock sold | Director		3
Management fees expense with related party						$ 200,000
Director fees with related party				100,000	100,000
Cinven | Maximum
Related Party Transaction [Line Items]
Travel expenses with related party				100,000	100,000	100,000
Medpace Investors
Related Party Transaction [Line Items]
Related party tax expense						800,000
Repayments of Related Party Debt						300,000
Proceeds from Related Party Debt						300,000
Employee Loans | Prepaid Expenses and Other Current Assets and Other Assets
Related Party Transaction [Line Items]
Employee advances receivables				$ 200,000	200,000
Service Agreements | Coherus Bio Sciences Inc
Related Party Transaction [Line Items]
Amount of investment								$ 2,500,000
Service agreement cancellation notice period				30 days
Revenue with related parties					8,000,000.0	22,300,000
Reimbursed out-of-pocket revenue with related parties					1,300,000	5,100,000
Reimbursed out-of-pocket expenses with related parties					1,300,000	5,100,000
Accounts receivable and unbilled, net					300,000
Advanced billings					1,500,000
Pre-funded study costs with related parties					1,000,000.0
Service Agreements | Xenon
Related Party Transaction [Line Items]
Revenue with related parties			$ 600,000			1,300,000
Reimbursed out-of-pocket revenue with related parties			100,000			200,000
Reimbursed out-of-pocket expenses with related parties			$ 100,000			200,000
Service Agreements | Cymabay
Related Party Transaction [Line Items]
Revenue with related parties					600,000	300,000
Accounts receivable and unbilled, net				$ 2,500,000	100,000
Service Agreements | Cymabay | Revenue Net
Related Party Transaction [Line Items]
Revenue with related parties				10,800,000
Service Agreements | LIB
Related Party Transaction [Line Items]
Revenue with related parties					1,400,000	$ 200,000
Accounts receivable and unbilled, net				1,000,000.0	500,000
Advanced billings				300,000	200,000
Service Agreements | LIB | Revenue Net
Related Party Transaction [Line Items]
Revenue with related parties				3,700,000
Service Agreements | CinRx Pharma and Subsidiaries
Related Party Transaction [Line Items]
Revenue with related parties					400,000
Accounts receivable and unbilled, net				400,000
Service Agreements | CinRx Pharma and Subsidiaries | Revenue Net
Related Party Transaction [Line Items]
Revenue with related parties				500,000
Service Agreements | The Summit
Related Party Transaction [Line Items]
Expenses incurred				$ 400,000
Purchase of Real Estate Properties | Chief Executive Officer
Related Party Transaction [Line Items]
Number of parcel in real estate property | Parcel						4
Purchase price of real estate property	$ 400,000
Transaction closed date	Jan. 11, 2017
Leased Real Estate
Related Party Transaction [Line Items]
Number of lease renewal, 10-year option | RenewalOption				2
Lease term upon renewal				10 years
Lease expiration year				2040
Leased Real Estate | Chief Executive Officer
Related Party Transaction [Line Items]
Term of lease				12 years
Lease expiration period				2022-11
Number of lease renewal, 10-year option | RenewalOption				1
Lease term upon renewal				10 years
Annual base rent				$ 2,200,000
Lease expense recognized				$ 2,200,000	2,100,000	$ 2,100,000
Storage space lease basis				month to month basis
Leased Real Estate | Chief Executive Officer And Immediate Family
Related Party Transaction [Line Items]
Number of lease renewal, 10-year option | RenewalOption				1
Lease expiration year				2027
Number of lease agreements | Agreement				2
Number of buildings | Building				2
Lease occupancy year				2012
Lease term upon renewal				10 years
Term of lease				15 years
Related party capital lease payments				$ 3,800,000	3,800,000	3,700,000
Deemed landlord liability, current				2,100,000	1,900,000
Deemed landlord liability, long-term portions				24,500,000	26,600,000
Leased Real Estate | Property and Equipment, Net | Chief Executive Officer And Immediate Family | Building
Related Party Transaction [Line Items]
Deemed assets, net				14,600,000	16,300,000
Travel Services | Chief Executive Officer
Related Party Transaction [Line Items]
Travel expenses with related party				1,300,000	1,100,000	$ 1,000,000.0
Accounts payable includes related parties				$ 200,000	$ 200,000