Fair Value of Financial Instruments (Recurring) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Interest Rate Swap [Member]
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Asset for interest rate swap agreements	$ 12,000	$ 5,400
Liability for interest rate swap agreements		(2,300)
Fair Value, Measurements, Recurring [Member]
Financial Assets:
Cash and cash equivalents	118,804	72,031
Restricted cash	7,565	17,943
Total Financial Assets	126,369	89,974
Financial Liabilities:
Contingent consideration	6,500
Total debt	1,780,547	1,622,811
Fair Value, Measurements, Recurring [Member] | Interest Rate Swap [Member]
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Asset for interest rate swap agreements	11,985	5,392
Liability for interest rate swap agreements		(2,283)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets:
Cash and cash equivalents	118,804	72,031
Restricted cash	0	0
Total Financial Assets	118,804	72,031
Financial Liabilities:
Contingent consideration	0
Total debt	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Interest Rate Swap [Member]
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Asset for interest rate swap agreements		0
Liability for interest rate swap agreements	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Assets:
Cash and cash equivalents	0	0
Restricted cash	7,565	17,943
Total Financial Assets	7,565	17,943
Financial Liabilities:
Contingent consideration	0
Total debt	1,780,547	1,622,811
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate Swap [Member]
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Asset for interest rate swap agreements	11,985	5,392
Liability for interest rate swap agreements		(2,283)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Assets:
Cash and cash equivalents	0	0
Restricted cash	0	0
Total Financial Assets	0	0
Financial Liabilities:
Contingent consideration	6,500
Total debt	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Interest Rate Swap [Member]
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Asset for interest rate swap agreements	$ 0	0
Liability for interest rate swap agreements		$ 0