Fair Value Measurements (Fair Value of Financial Assets and Liabilities) (Details 1) - USD ($) $ in Thousands		Mar. 31, 2022	Dec. 31, 2021
Assets
Marketable equity securities		$ 801,178	$ 809,997
Fair Value, Recurring [Member]
Assets
Marketable equity securities	[1]	801,178	809,997
Other current investments	[2]	15,788	14,448
Total Financial Assets		816,966	824,445
Liabilities
Contingent consideration liabilities	[3]	14,954	14,881
Interest rate swap	[4]	453	2,049
Foreign exchange swap	[5]		484
Mandatorily redeemable noncontrolling interest	[6]	17,031	13,661
Total Financial Liabilities		32,438	31,075
Level 1 | Fair Value, Recurring [Member]
Assets
Marketable equity securities	[1]	801,178	809,997
Other current investments	[2]	9,690	7,230
Total Financial Assets		810,868	817,227
Liabilities
Contingent consideration liabilities	[3]	0	0
Interest rate swap	[4]	0	0
Foreign exchange swap	[5]		0
Mandatorily redeemable noncontrolling interest	[6]	0	0
Total Financial Liabilities		0	0
Level 2 | Fair Value, Recurring [Member]
Assets
Marketable equity securities	[1]	0	0
Other current investments	[2]	6,098	7,218
Total Financial Assets		6,098	7,218
Liabilities
Contingent consideration liabilities	[3]	0	0
Interest rate swap	[4]	453	2,049
Foreign exchange swap	[5]		484
Mandatorily redeemable noncontrolling interest	[6]	0	0
Total Financial Liabilities		453	2,533
Level 3 | Fair Value, Recurring [Member]
Assets
Marketable equity securities	[1]	0	0
Other current investments	[2]	0	0
Total Financial Assets		0	0
Liabilities
Contingent consideration liabilities	[3]	14,954	14,881
Interest rate swap	[4]	0	0
Foreign exchange swap	[5]		0
Mandatorily redeemable noncontrolling interest	[6]	17,031	13,661
Total Financial Liabilities		$ 31,985	$ 28,542

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

[2] 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.

[3] Included in Accounts 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.

[4] Included in Other Liabilities. 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 and accrued liabilities, and valued based on a valuation model that calculates the differential between the contract price and the market-based forward rate.

[6] The fair value of the mandatorily redeemable noncontrolling interest is based on the fair value of the underlying subsidiaries owned by GHC One, 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.