Fair Value Measurements and Derivative Instruments (Recurring) (Details) (Fair Value, Measurements, Recurring, USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Total
Assets:
Derivative financial instruments	$ 188,576	$ 96,489
Investments	6,044	6,231
Total Assets	194,620	102,720
Liabilities:
Derivative financial instruments	100,260	85,119
Total Liabilities	100,260	85,119
Level 1
Assets:
Derivative financial instruments	0	0
Investments	6,044	6,231
Total Assets	6,044	6,231
Liabilities:
Derivative financial instruments	0	0
Total Liabilities	0	0
Level 2
Assets:
Derivative financial instruments	188,576	96,489
Investments	0	0
Total Assets	188,576	96,489
Liabilities:
Derivative financial instruments	100,260	85,119
Total Liabilities	100,260	85,119
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