Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	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, Inputs, Level 2 [Member] | Interest Rate Swap [Member]
Derivative Instruments and Hedging Disclosure:
Asset for interest rate swap agreements	$ 6,268
Liability for swap	601
Fair Value, Measurements, Recurring [Member]
Financial Assets:
Cash and cash equivalents	89,422	72,031
Restricted cash	17,435	17,943
Call Option Fair Value	4,628
Total Financial Assets	111,485	89,974
Financial Liabilities:
Total debt	1,659,268	1,622,811
Fair Value, Measurements, Recurring [Member] | Interest Rate Swap [Member]
Derivative Instruments and Hedging Disclosure:
Asset for interest rate swap agreements	6,268	5,392
Liability for swap	601	2,283
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets:
Cash and cash equivalents	89,422	72,031
Restricted cash	0	0
Call Option Fair Value	0
Total Financial Assets	89,422	72,031
Financial Liabilities:
Total debt	0	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	17,435	17,943
Call Option Fair Value	0
Total Financial Assets	17,435	17,943
Financial Liabilities:
Total debt	1,659,268	1,622,811
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		5,392
Liability for swap		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
Call Option Fair Value	4,628
Total Financial Assets	4,628	0
Financial Liabilities:
Total debt	0	0
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