Debt (Narrative) (Details)										1 Months Ended	3 Months Ended								12 Months Ended
		Jan. 26, 2021 USD ($)	Dec. 31, 2020 USD ($)	Jun. 29, 2020 GBP (£)	Dec. 02, 2019 USD ($)	Jan. 31, 2019 USD ($)	Jun. 29, 2018 USD ($)	May 30, 2018 USD ($)	Jun. 29, 2015	Jun. 30, 2018 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2020 GBP (£)
Debt Instrument [Line Items]
Debt extinguishment costs																			$ 0	$ 0	$ (11,378,000)
Average borrowings outstanding																			$ 512,400,000	$ 500,600,000
Average annual interest rate of borrowings																			5.10%	5.10%
Interest expense																			$ (34,439,000)	$ (23,628,000)	(32,549,000)
Interest income											$ 876,000	$ 890,000	$ 954,000	$ 1,151,000	$ 1,398,000	$ 1,474,000	$ 1,579,000	$ 1,700,000	3,871,000	6,151,000	5,353,000
Interest expense											16,008,000	$ 7,247,000	$ 7,377,000	$ 7,678,000	$ 7,192,000	$ 6,776,000	$ 8,386,000	$ 7,425,000	38,310,000	$ 29,779,000	$ 37,902,000
7.25% Unsecured Notes due February 1, 2019 [Member]
Debt Instrument [Line Items]
Interest rate							7.25%
Redemption of notes outstanding							$ 400,000,000
Debt extinguishment costs							$ 11,400,000
Other Indebtedness [Member]
Debt Instrument [Line Items]
Interest rate															2.00%					2.00%
5.75% Unsecured Notes due June 1, 2026 [Member]
Debt Instrument [Line Items]
Unamortized debt issuance costs			$ 3,900,000								$ 3,900,000				$ 4,600,000				$ 3,900,000	$ 4,600,000
Interest rate			5.75%					5.75%			5.75%				5.75%				5.75%	5.75%		5.75%
Debt instrument, face amount								$ 400,000,000
Fair value of debt instrument			$ 421,700,000								$ 421,700,000				$ 427,700,000				$ 421,700,000	$ 427,700,000
Carrying value of debt instrument	[1]		396,112,000								396,112,000				395,393,000				396,112,000	395,393,000
Kaplan Four Year Credit Agreement Dated July 14, 2016 [Member]
Debt Instrument [Line Items]
Unamortized debt issuance costs															100,000					100,000
Line of credit facility outstanding	[2]		0								0				78,650,000				0	78,650,000
Five Year Revolving Credit Agreement Dated June 29, 2015 [Member]
Debt Instrument [Line Items]
Debt Instrument, Term									5 years
Five-Year Credit Agreement dated May 30, 2018 [Member]
Debt Instrument [Line Items]
Line of credit facility outstanding			74,686,000								74,686,000				0				74,686,000	0
Debt Instrument, Term								5 years
Credit facility current borrowing capacity								$ 300,000,000
Debt covenant net leverage ratio, maximum								3.5
Debt covenant interest coverage ratio, minimum								3.5
Multicurrency $100 million portion of revolver [Member]
Debt Instrument [Line Items]
Credit facility current borrowing capacity								$ 100,000,000
USD $200 million portion of revolver [Member]
Debt Instrument [Line Items]
Credit facility current borrowing capacity								$ 200,000,000
Pinnacle Bank Term Loan [Member]
Debt Instrument [Line Items]
Loans Payable to Bank			10,692,000								10,692,000				11,203,000				10,692,000	11,203,000
Pinnacle Bank Line Of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility outstanding			2,295,000								2,295,000				0				2,295,000	0
Commercial note with Truist Bank [Member]
Debt Instrument [Line Items]
Notes Payable to Bank			$ 25,250,000								$ 25,250,000				$ 27,500,000				$ 25,250,000	27,500,000
Minimum [Member] | Other Indebtedness [Member]
Debt Instrument [Line Items]
Interest rate			0.00%								0.00%								0.00%			0.00%
Minimum [Member] | Five-Year Credit Agreement dated May 30, 2018 [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage								0.15%
Maximum [Member] | Other Indebtedness [Member]
Debt Instrument [Line Items]
Interest rate			16.00%								16.00%								16.00%			16.00%
Maximum [Member] | Five-Year Credit Agreement dated May 30, 2018 [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage								0.25%
Eurodollar [Member] | Five-Year Credit Agreement dated May 30, 2018 [Member]
Debt Instrument [Line Items]
Applicable interest rate margin								1.00%
Fed Funds Effective Rate Overnight Index Swap Rate [Member] | Five-Year Credit Agreement dated May 30, 2018 [Member]
Debt Instrument [Line Items]
Applicable interest rate margin								0.50%
Education [Member] | Five-Year Credit Agreement dated May 30, 2018 [Member]
Debt Instrument [Line Items]
Proceeds from Lines of Credit | £				£ 60,000,000
Line of credit facility outstanding | £																						£ 55,000,000
Education [Member] | London Interbank Offered Rate (LIBOR) [Member] | Five-Year Credit Agreement dated May 30, 2018 [Member]
Debt Instrument [Line Items]
Applicable interest rate margin			1.50%
Graham Healthcare Group [Member]
Debt Instrument [Line Items]
Interest expense										$ 6,200,000
Graham Healthcare Group [Member] | Pinnacle Bank Term Loan [Member]
Debt Instrument [Line Items]
Interest rate					4.35%
Loans Payable to Bank					$ 11,250,000
Debt Instrument, Term					5 years
Graham Healthcare Group [Member] | Pinnacle Bank Term Loan [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Interest rate		4.15%
Loans Payable to Bank		$ 10,600,000
Graham Healthcare Group [Member] | Pinnacle Bank Line Of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility outstanding			$ 2,300,000								$ 2,300,000								$ 2,300,000
Line of Credit Facility, Maximum Borrowing Capacity					$ 2,250,000
Debt Instrument, Term					2 years
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage					0.25%
Graham Healthcare Group [Member] | Pinnacle Bank Line Of Credit [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Interest rate		3.25%
Line of Credit Facility, Maximum Borrowing Capacity		$ 6,000,000.0
Debt Instrument, Term		2 years
Graham Healthcare Group [Member] | London Interbank Offered Rate (LIBOR) [Member] | Pinnacle Bank Line Of Credit [Member]
Debt Instrument [Line Items]
Applicable interest rate margin			2.75%		2.75%
Graham Healthcare Group [Member] | London Interbank Offered Rate (LIBOR) [Member] | Pinnacle Bank Line Of Credit [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Applicable interest rate margin		2.75%
Securities Subject to Mandatory Redemption [Member] | Graham Healthcare Group [Member]
Debt Instrument [Line Items]
Interest income																				$ 100,000
Interest expense										$ 6,200,000									$ 8,500,000
Automotive [Member] | Interest Rate Swap [Member]
Debt Instrument [Line Items]
Derivative, Notional Amount						$ 30,000,000
Derivative, Fixed Interest Rate						2.70%
Derivative, Total Fixed Interest Rate						4.70%
Derivative, Basis Spread on Variable Rate						2.00%
Automotive [Member] | Commercial note with Truist Bank [Member]
Debt Instrument [Line Items]
Debt Instrument, Term						10 years
Notes Payable to Bank						$ 30,000,000
Debt Instrument, Periodic Payment, Principal						$ 250,000
Automotive [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member] | Commercial note with Truist Bank [Member]
Debt Instrument [Line Items]
Applicable interest rate margin						1.75%
Automotive [Member] | London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member] | Commercial note with Truist Bank [Member]
Debt Instrument [Line Items]
Applicable interest rate margin						2.00%

[1] The carrying value is net of $3.9 million and $4.6 million of unamortized debt issuance costs as of December 31, 2020 and 2019, respectively.

[2] The carrying value is net of $0.1 million of unamortized debt issuance costs as of December 31, 2019.