Relationship with Universal Health Realty Income Trust and Related Party Transactions - Additional Information (Detail)	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($) Facility $ / shares	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($) SquareFoot	Dec. 31, 2013	Sep. 30, 2020 USD ($) Hospital Facility SquareFoot Bed Lease	Sep. 30, 2019 USD ($) Hospital	Dec. 31, 2019 USD ($)	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Net revenues	$ 2,912,541,000		$ 2,822,453,000		$ 8,471,962,000	$ 8,482,012,000
Number of hospital facilities | Hospital					3
Number of third party tenant rentable square feet | SquareFoot					26,000
Number of flex lease commitment rentable square feet | SquareFoot					20,000
Chief Executive Officer
Related Party Transaction [Line Items]
Estimated payments to acquire life insurance policies					$ 28,000,000
Payments to acquire life insurance policies, net					1,100,000		$ 1,100,000
Chief Executive Officer | Trust Owned by CEO
Related Party Transaction [Line Items]
Estimated payments to acquire life insurance policies					$ 9,000,000
Joint Venture Agreement
Related Party Transaction [Line Items]
Lease initial terms	20 years				20 years
Lease renewal period, years					10 years
Number of beds | Bed					108
Number of triple net lease | Lease					5
Number of square foot to be constructed | SquareFoot					80,000
Expected aggregate fee					$ 750,000
Estimated project cost					37,500,000
Estimated initial annual rent					$ 2,700,000
Expected project to begin and be completed year					2020
Southwest Healthcare System, Inland Valley Campus
Related Party Transaction [Line Items]
End of Lease Term					2021-12
Annual Minimum Rent					$ 2,648,000
Minimum
Related Party Transaction [Line Items]
Lease initial terms	5 years				5 years
Minimum | Chief Executive Officer
Related Party Transaction [Line Items]
Estimated death benefit proceeds					$ 37,000,000
Maximum
Related Party Transaction [Line Items]
Lease initial terms	10 years				10 years
Maximum | Joint Venture Agreement
Related Party Transaction [Line Items]
Expected project to begin and be completed year					2021
Relationship with Universal Health Realty Income Trust
Related Party Transaction [Line Items]
Trust outstanding shares held, percentage	5.70%				5.70%
Percentage of advisory fee on average invested real estate assets	0.70%		0.70%		0.70%	0.70%	0.70%	0.70%	0.70%
Pre-tax share of income from the Trust	$ 300,000		$ 300,000		$ 800,000	$ 700,000
Dividends received from the Trust	543,000		536,000		1,600,000	1,600,000
Carrying value of investment in Trust	5,600,000	$ 6,400,000			5,600,000		$ 6,400,000
Market value of investment in Trust	$ 44,900,000	92,400,000			$ 44,900,000		$ 92,400,000
Lease initial terms	10 years				10 years
Lease renewal period, years					5 years
Rent expense under operating leases	$ 4,000,000		$ 4,000,000		$ 12,000,000	$ 12,000,000
Notice period on renewal of lease					90 days
Period of rights of refusal to leased facilities					180 days
Number of hospital facilities | Hospital					3	3
Number of free-standing emergency departments to be acquired | Facility	2				2
Number of square feet to be constructed | SquareFoot			75,000
Percentage of master lease rentable square feet					50.00%
Annual Minimum Rent					$ 644,000
Relationship with Universal Health Realty Income Trust | Minimum
Related Party Transaction [Line Items]
Lease initial terms	13 years				13 years
Relationship with Universal Health Realty Income Trust | Minimum | Limited Liability Companies
Related Party Transaction [Line Items]
Non-controlling ownership interests by subsidiaries	95.00%				95.00%
Relationship with Universal Health Realty Income Trust | Maximum
Related Party Transaction [Line Items]
Lease initial terms	15 years				15 years
Relationship with Universal Health Realty Income Trust | Maximum | Limited Liability Companies
Related Party Transaction [Line Items]
Non-controlling ownership interests by subsidiaries	100.00%				100.00%
Relationship with Universal Health Realty Income Trust | Advisory Fee
Related Party Transaction [Line Items]
Net revenues	$ 1,000,000.0		$ 1,000,000.0		$ 3,100,000	$ 3,000,000.0
Premier, Inc.
Related Party Transaction [Line Items]
Cash dividend declared per share | $ / shares	$ 0.19
Premier, Inc. | Other (Income) Expense, Net
Related Party Transaction [Line Items]
Dividend	$ 400,000
Premier, Inc. | Other (Income) Expense, Net | ASU 2016-01
Related Party Transaction [Line Items]
Unrealized gain					9,000,000
Premier, Inc. | Group Purchasing Organization Agreement | Restricted Stock
Related Party Transaction [Line Items]
Shares vesting period				7 years
Shares vesting period start year				2014
Shares vesting period end year				2020
Market value of retained vested shares		$ 70,000,000			$ 61,000,000