Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Interest Rate Swap [Member]
Derivative Instruments and Hedging Disclosure:
Asset for interest rate swap agreements			$ 5,400
Liability for swap			2,300
Fair Value, Measurements, Recurring [Member]
Financial Assets:
Cash and cash equivalents	$ 149,411		72,031
Restricted cash	13,532		17,943
Total Financial Assets	162,943		89,974
Financial Liabilities:
Contingent consideration	1,800
Total debt	1,825,984		1,622,811
Financial and Nonfinancial Liabilities, Fair Value Disclosure	1,827,784
Fair Value, Measurements, Recurring [Member] | Interest Rate Swap [Member]
Derivative Instruments and Hedging Disclosure:
Asset for interest rate swap agreements	5,951		5,392
Liability for swap	217		2,283
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets:
Cash and cash equivalents	149,411		72,031
Restricted cash	0		0
Total Financial Assets	149,411		72,031
Financial Liabilities:
Contingent consideration	0
Total debt	0		0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Interest Rate Swap [Member]
Derivative Instruments and Hedging Disclosure:
Asset for interest rate swap agreements	0		0
Liability for swap	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Assets:
Cash and cash equivalents	0		0
Restricted cash	13,532		17,943
Total Financial Assets	13,532		17,943
Financial Liabilities:
Contingent consideration	0
Total debt	1,825,984		1,622,811
Financial and Nonfinancial Liabilities, Fair Value Disclosure	1,825,984
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate Swap [Member]
Derivative Instruments and Hedging Disclosure:
Asset for interest rate swap agreements	5,951		5,392
Liability for swap	217		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	1,800
Total debt	0		0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	1,800
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Interest Rate Swap [Member]
Derivative Instruments and Hedging Disclosure:
Asset for interest rate swap agreements	0		0
Liability for swap	0		$ 0
Maximum [Member]
Financial Liabilities:
Contingent consideration	$ 3,000
Mercury, Inc. [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Call Option Fair Value		$ 4,600