Derivative Financial Instruments - Offsetting of Derivative Assets and Liabilities (Details) - Zero Cost Collars [Member] - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Asset Derivatives:
Asset Derivatives, Gross amounts of recognized assets/liabilities	$ 13
Asset Derivatives, Gross amounts offset in the balance sheets	0
Asset Derivatives, Net amounts of assets/liabilities presented in the balance sheets	13
Asset Derivatives, Gross amounts not offset in the balance sheets, Financial instruments	0
Asset Derivatives, Gross amounts not offset in the balance sheets, Cash collateral pledged	0
Asset Derivatives, Net amount	13
Liability Derivatives:
Liability Derivatives, Gross amounts of recognized liabilities	2,234	$ 117
Liability Derivatives, Gross amounts offset in the balance sheets	0	0
Liability Derivatives, Net amounts of liabilities presented in the balance sheets	2,234	117
Liability Derivatives, Gross amounts not offset in the balance sheets, Financial instruments	0	0
Liability Derivatives, Gross amounts not offset in the balance sheets, Cash collateral pledged	(590)	360
Liability Derivatives, Net amount after master netting	$ 1,644	$ 243