Fair Value Measurements (Fair Value of Financial Assets and Liabilities) (Details 1) - USD ($) $ in Thousands		Sep. 30, 2023	Dec. 31, 2022
Assets
Money Market Investments		$ 39,700	$ 7,700
Marketable equity securities		665,514	609,921
Fair Value, Recurring [Member]
Assets
Money Market Investments	[1]	39,740	7,686
Marketable equity securities	[2]	665,514	609,921
Other current investments	[3]	6,832	12,487
Interest Rate Swaps	[4]		2,636
Total Financial Assets		712,086	632,730
Liabilities
Contingent consideration liabilities	[5]	3,080	8,423
Interest rate swap	[6]	733
Foreign exchange swap	[7]		333
Mandatorily redeemable noncontrolling interest	[8]	32,043	30,845
Total Financial Liabilities		35,856	39,601
Level 1 | Fair Value, Recurring [Member]
Assets
Money Market Investments	[1]	0	0
Marketable equity securities	[2]	665,514	609,921
Other current investments	[3]	6,799	7,471
Interest Rate Swaps	[4]		0
Total Financial Assets		672,313	617,392
Liabilities
Contingent consideration liabilities	[5]	0	0
Interest rate swap	[6]	0
Foreign exchange swap	[7]		0
Mandatorily redeemable noncontrolling interest	[8]	0	0
Total Financial Liabilities		0	0
Level 2 | Fair Value, Recurring [Member]
Assets
Money Market Investments	[1]	39,740	7,686
Marketable equity securities	[2]	0	0
Other current investments	[3]	33	5,016
Interest Rate Swaps	[4]		2,636
Total Financial Assets		39,773	15,338
Liabilities
Contingent consideration liabilities	[5]	0	0
Interest rate swap	[6]	733
Foreign exchange swap	[7]		333
Mandatorily redeemable noncontrolling interest	[8]	0	0
Total Financial Liabilities		733	333
Level 3 | Fair Value, Recurring [Member]
Assets
Money Market Investments	[1]	0	0
Marketable equity securities	[2]	0	0
Other current investments	[3]	0	0
Interest Rate Swaps	[4]		0
Total Financial Assets		0	0
Liabilities
Contingent consideration liabilities	[5]	3,080	8,423
Interest rate swap	[6]	0
Foreign exchange swap	[7]		0
Mandatorily redeemable noncontrolling interest	[8]	32,043	30,845
Total Financial Liabilities		$ 35,123	$ 39,268

[1] The Company’s money market investments are included in cash and cash equivalents and the value considers the liquidity of the counterparty.

[2] The Company’s investments in marketable equity securities are held in common shares of U.S. corporations that are actively traded on U.S. stock exchanges. Price quotes for these shares are readily available.

[3] Includes U.S. Government Securities, corporate bonds, mutual funds and time deposits. These investments are valued using a market approach based on the quoted market prices of the security or inputs that include quoted market prices for similar instruments and are classified as either Level 1 or Level 2 in the fair value hierarchy.

[4] Included in Deferred charges and other assets. The Company utilized a market approach model using the notional amount of the interest rate swap multiplied by the observable inputs of time to maturity and market interest rates.

[5] Included in Accounts payable, vehicle floor plan payable and accrued liabilities and Other Liabilities. The Company determined the fair value of the contingent consideration liabilities using either a Monte Carlo simulation, Black-Scholes model, or probability-weighted analysis depending on the type of target included in the contingent consideration requirements (revenue, EBITDA, client retention). All analyses included estimated financial projections for the acquired businesses and acquisition-specific discount rates.

[6] Included in Other Liabilities. The Company utilized a market approach model using the notional amount of the interest rate swaps multiplied by the observable inputs of time to maturity and market interest rates.

[7] Included in Accounts payable, vehicle floor plan payable and accrued liabilities, and valued based on a valuation model that calculates the differential between the contract price and the market-based forward rate.

[8] The fair value of the mandatorily redeemable noncontrolling interest is based on the fair value of the underlying subsidiaries owned by GHC One and GHC Two, after taking into account any debt and other noncontrolling interests of its subsidiary investments. The fair value of the owned subsidiaries is determined using enterprise value analyses which include an equal weighing between guideline public company and discounted cash flow analyses.