Fair Value of Financial Instruments, Assests and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Oct. 01, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, assets	$ 2,346	$ 3,126	$ 2,866
Derivatives, assets	20,079	12,226	11,975
Total assets, fair value hierarchy	22,425	15,352	14,841
Derivatives, liabilities	2,113	23,051	22,671
Option Agreement	23,460	23,980	28,510
Total Liabilities	$ 25,573	47,031	51,181
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	45 days
Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	30 days
Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	90 days
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, assets	$ 2,346	3,126	2,866
Derivatives, assets	0	0	0
Total assets, fair value hierarchy	2,346	3,126	2,866
Derivatives, liabilities	0	0	0
Option Agreement	0	0	0
Total Liabilities	0	0	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, assets	0	0	0
Derivatives, assets	20,079	12,226	11,975
Total assets, fair value hierarchy	20,079	12,226	11,975
Derivatives, liabilities	2,113	23,051	22,671
Option Agreement	0	0	0
Total Liabilities	2,113	23,051	22,671
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, assets	0	0	0
Derivatives, assets	0	0	0
Total assets, fair value hierarchy	0	0	0
Derivatives, liabilities	0	0	0
Option Agreement	23,460	23,980	28,510
Total Liabilities	$ 23,460	$ 23,980	$ 28,510