Fair Value of Financial Instruments (Fair Value of Financial Instruments) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Financial Liabilities:
Contingent consideration						$ 6,200
Derivatives:
Increase/(decrease) in contingent consideration value	$ (600)	$ (1,500)	$ (200)	$ (1,100)
Fair value adjustment of minority owned equity investment	4,300		6,600
Interest Rate Swap
Derivatives:
Asset for Swaps					$ 13,300
Recurring
Financial Assets:
Cash and cash equivalents	82,042		82,042		85,271
Restricted cash	13,686		13,686		12,979
Other investments	1,898		1,898		7,930
Total	97,626		97,626		106,180
Financial Liabilities:
Contingent consideration	4,904		4,904		5,700
Total debt	1,783,906		1,783,906		1,797,597
Total	1,788,810		1,788,810		1,803,297
Recurring | Interest Rate Swap
Derivatives:
Asset for Swaps	2,187		2,187		13,344
Derivative Liability	48,483		48,483		15,188
Recurring | Level 1
Financial Assets:
Cash and cash equivalents	82,042		82,042		85,271
Restricted cash	2,515		2,515		1,366
Other investments	0		0		0
Total	84,557		84,557		86,637
Financial Liabilities:
Contingent consideration	0		0		0
Total debt	0		0		0
Total	0		0		0
Recurring | Level 1 | Interest Rate Swap
Derivatives:
Asset for Swaps	0		0		0
Derivative Liability	0		0		0
Recurring | Level 2
Financial Assets:
Cash and cash equivalents	0		0		0
Restricted cash	11,171		11,171		11,613
Other investments	1,898		1,898		0
Total	13,069		13,069		11,613
Financial Liabilities:
Contingent consideration	0		0		0
Total debt	1,783,906		1,783,906		1,797,597
Total	1,783,906		1,783,906		1,797,597
Recurring | Level 2 | Interest Rate Swap
Derivatives:
Asset for Swaps	2,187		2,187		13,344
Derivative Liability	48,483		48,483		15,188
Recurring | Level 3
Financial Assets:
Cash and cash equivalents	0		0		0
Restricted cash	0		0		0
Other investments	0		0		7,930
Total	0		0		7,930
Financial Liabilities:
Contingent consideration	4,904		4,904		5,700
Total debt	0		0		0
Total	4,904		4,904		5,700
Recurring | Level 3 | Interest Rate Swap
Derivatives:
Asset for Swaps	0		0		0
Derivative Liability	$ 0		$ 0		$ 0
Maximum | Myriad Development, Inc. & Insignificant Acquisition
Financial Liabilities:
Contingent consideration						$ 20,500