Fair Value Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Level 1 [Member]
Assets:
Total	$ 0	$ 0
Liabilities:
Interest rate derivative financial instruments	0	0
Total	0	0
Level 2 [Member]
Assets:
Total	7,562	32,587
Liabilities:
Interest rate derivative financial instruments	29,871	28,653
Total	29,871	28,653
Total
Assets:
Total	7,562	32,587
Liabilities:
Interest rate derivative financial instruments	29,871	28,653
Total	29,871	28,653
Investments [Member] | Level 1 [Member]
Assets:
Investments, Fair Value Disclosure		0
Investments [Member] | Level 2 [Member]
Assets:
Investments, Fair Value Disclosure	7,450	12,283
Investments [Member] | Total
Assets:
Investments, Fair Value Disclosure	7,450	12,283
Demand Obligation [Member] | Level 1 [Member]
Assets:
Investments, Fair Value Disclosure	0	0
Demand Obligation [Member] | Level 2 [Member]
Assets:
Investments, Fair Value Disclosure	112	20,304
Demand Obligation [Member] | Total
Assets:
Investments, Fair Value Disclosure	$ 112	$ 20,304