Debt (Narrative) (Details)					1 Months Ended	3 Months Ended								12 Months Ended
		Jun. 29, 2018 USD ($)	May 30, 2018 USD ($)	Jul. 14, 2016 GBP (£)	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jul. 25, 2016 GBP (£)
Debt Instrument [Line Items]
Debt extinguishment costs						$ 0	$ 0	$ (11,378,000)	$ 0					$ (11,378,000)	$ 0	$ 0
Average borrowings outstanding														$ 517,200,000	$ 493,200,000
Weighted average interest rate of borrowings														5.60%	6.30%
Interest expense														$ (32,549,000)	$ (27,305,000)	(32,297,000)
Interest income						1,469,000	611,000	1,901,000	1,372,000	$ 3,184,000	$ 861,000	$ 1,173,000	$ 1,363,000	5,353,000	6,581,000	3,093,000
Interest expense						$ 6,531,000	$ 6,135,000	$ 17,165,000	$ 8,071,000	$ 8,103,000	$ 8,619,000	$ 9,035,000	$ 8,129,000	$ 37,902,000	$ 33,886,000	35,390,000
7.25% Unsecured Notes due February 1, 2019 [Member]
Debt Instrument [Line Items]
Interest rate		7.25%				7.25%				7.25%				7.25%	7.25%
Redemption of notes outstanding		$ 400,000,000
Debt extinguishment costs		$ 11,400,000
Fair value of debt instrument										$ 414,700,000					$ 414,700,000
Carrying value of debt instrument						$ 0				$ 399,507,000				$ 0	$ 399,507,000
Other Indebtedness [Member]
Debt Instrument [Line Items]
Interest rate						2.00%				2.00%				2.00%	2.00%
Maturity year														Dec. 31, 2026	Dec. 31, 2026
5.75% Unsecured Notes due June 1, 2026 [Member]
Debt Instrument [Line Items]
Unamortized debt issuance costs						$ 5,300,000								$ 5,300,000
Interest rate			5.75%
Debt instrument, face amount			$ 400,000,000
Fair value of debt instrument						406,700,000								406,700,000
Carrying value of debt instrument	[1]					394,675,000				$ 0				394,675,000	$ 0
Kaplan Four Year Credit Agreement Dated July 14, 2016 [Member]
Debt Instrument [Line Items]
Unamortized debt issuance costs						200,000				400,000				200,000	400,000
Line of Credit	[2]					82,366,000				93,671,000				82,366,000	93,671,000
Five-Year Revolving Credit Agreement Dated June 29, 2015 [Member]
Debt Instrument [Line Items]
Line of Credit										$ 0					0
Five-Year Credit Agreement dated May 30, 2018 [Member]
Debt Instrument [Line Items]
Credit facility current borrowing capacity			$ 300,000,000
Line of Credit						$ 0								$ 0
Debt covenant net leverage ratio, maximum			3.5
Debt covenant interest coverage ratio, minimum			3.5
Debt Instrument, Term			5 years
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
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] | 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%
Federal Funds Effective Swap Rate [Member] | Five-Year Credit Agreement dated May 30, 2018 [Member]
Debt Instrument [Line Items]
Applicable interest rate margin			0.50%
Education [Member] | Interest Rate Swap [Member]
Debt Instrument [Line Items]
Derivative, Notional Amount | £																	£ 75,000,000
Interest rate swap percentage rate																	2.01%
Derivative, Fixed Interest Rate																	0.51%
Basis Spread on Variable Rate																	1.50%
Education [Member] | Kaplan Four Year Credit Agreement Dated July 14, 2016 [Member]
Debt Instrument [Line Items]
Credit facility current borrowing capacity | £																	£ 75,000,000
Line of Credit | £				£ 75,000,000
Debt covenant net leverage ratio, maximum				3.5
Debt covenant interest coverage ratio, minimum				3.5
Debt Instrument, Term				4 years
Education [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member] | Kaplan Four Year Credit Agreement Dated July 14, 2016 [Member]
Debt Instrument [Line Items]
Applicable interest rate margin				1.25%
Education [Member] | London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member] | Kaplan Four Year Credit Agreement Dated July 14, 2016 [Member]
Debt Instrument [Line Items]
Applicable interest rate margin				1.75%
Debt Instrument, Redemption, First Anniversary [Member] | Education [Member] | Kaplan Four Year Credit Agreement Dated July 14, 2016 [Member]
Debt Instrument [Line Items]
Debt Instrument Price Percentage Of Outstanding Balance Redeemed				6.66%
Debt Instrument, Redemption, Second Anniversary [Member] | Education [Member] | Kaplan Four Year Credit Agreement Dated July 14, 2016 [Member]
Debt Instrument [Line Items]
Debt Instrument Price Percentage Of Outstanding Balance Redeemed				6.66%
Debt Instrument, Redemption, Third Anniversary [Member] | Education [Member] | Kaplan Four Year Credit Agreement Dated July 14, 2016 [Member]
Debt Instrument [Line Items]
Debt Instrument Price Percentage Of Outstanding Balance Redeemed				6.66%
Securities Subject to Mandatory Redemption [Member]
Debt Instrument [Line Items]
Interest income															$ 2,300,000
Interest expense																$ 2,700,000
Securities Subject to Mandatory Redemption [Member] | Graham Healthcare Group [Member]
Debt Instrument [Line Items]
Interest expense					$ 6,200,000

[1] The carrying value is net of $5.3 million of unamortized debt issuance costs as of December 31, 2018.

[2] The carrying value is net of $0.2 million and $0.4 million of unamortized debt issuance costs as of December 31, 2018 and 2017, respectively.