Fair Value Measurements and Derivative Instruments (Recurring) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Assets:
Derivative financial instruments	$ 0	$ 4,759
Liabilities:
Derivative financial instruments	346,887	914,477
Fair Value, Measurements, Recurring | Total Fair Value
Assets:
Derivative financial instruments	19,397	134,574
Investments	3,576	3,965
Total Assets	22,973	138,539
Liabilities:
Derivative financial instruments	373,497	1,044,292
Total Liabilities	373,497	1,044,292
Fair Value, Measurements, Recurring | Level 1
Assets:
Derivative financial instruments	0	0
Investments	3,576	3,965
Total Assets	3,576	3,965
Liabilities:
Derivative financial instruments	0	0
Total Liabilities	0	0
Fair Value, Measurements, Recurring | Level 2
Assets:
Derivative financial instruments	19,397	134,574
Investments	0	0
Total Assets	19,397	134,574
Liabilities:
Derivative financial instruments	373,497	1,044,292
Total Liabilities	373,497	1,044,292
Fair Value, Measurements, Recurring | Level 3
Assets:
Derivative financial instruments	0	0
Investments	0	0
Total Assets	0	0
Liabilities:
Derivative financial instruments	0	0
Total Liabilities	$ 0	$ 0