Fair Value of Financial Instruments (Fair Value of Financial Instruments) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Derivatives:
Increase/(decrease) in contingent consideration value	$ 100	$ (200)	$ (1,000)
Fair value adjustment of minority owned equity investment		6,600
Interest Rate Swap
Derivatives:
Asset for Swaps				$ 13,300
Recurring
Financial Assets:
Cash and cash equivalents		88,238		85,271
Restricted cash		13,618		12,979
Other investments		1,825		7,930
Total		103,681		106,180
Financial Liabilities:
Contingent consideration		4,895		5,700
Total debt		1,731,066		1,797,597
Total		1,735,961		1,803,297
Recurring | Interest Rate Swap
Derivatives:
Asset for Swaps		1,218		13,344
Derivative Liability		58,335		15,188
Recurring | Level 1
Financial Assets:
Cash and cash equivalents		88,238		85,271
Restricted cash		2,526		1,366
Other investments		0		0
Total		90,764		86,637
Financial Liabilities:
Contingent consideration		0		0
Total debt		0		0
Total		0		0
Recurring | Level 1 | Interest Rate Swap
Derivatives:
Asset for Swaps		0		0
Derivative Liability		0		0
Recurring | Level 2
Financial Assets:
Cash and cash equivalents		0		0
Restricted cash		11,092		11,613
Other investments		1,825		0
Total		12,917		11,613
Financial Liabilities:
Contingent consideration		0		0
Total debt		1,731,066		1,797,597
Total		1,731,066		1,797,597
Recurring | Level 2 | Interest Rate Swap
Derivatives:
Asset for Swaps		1,218		13,344
Derivative Liability		58,335		15,188
Recurring | Level 3
Financial Assets:
Cash and cash equivalents		0		0
Restricted cash		0		0
Other investments		0		7,930
Total		0		7,930
Financial Liabilities:
Contingent consideration		4,895		5,700
Total debt		0		0
Total		4,895		5,700
Recurring | Level 3 | Interest Rate Swap
Derivatives:
Asset for Swaps		0		0
Derivative Liability		$ 0		$ 0
Myriad Development, Inc. & Insignificant Acquisition
Financial Liabilities:
Contingent consideration					$ 6,200
Maximum | Myriad Development, Inc. & Insignificant Acquisition
Financial Liabilities:
Contingent consideration					$ 20,500