Derivative Instruments - Gross and Net Derivative Positions, Including Pledged Collateral (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Offsetting Derivative Assets
Gross amounts recognized	$ 659	$ 1,620
Gross amounts offset in the Consolidated Balance Sheets	0	0
Net amounts presented in the Consolidated Balance Sheets	659	1,620
Financial instruments	659	1,620
Financial collateral pledged	0	0
Net amounts	0	0
Offsetting Derivative Liabilities
Gross amounts recognized	7,719	6,768
Gross amounts offset in the Consolidated Balance Sheets	0	0
Net amounts presented in the Consolidated Balance Sheets	7,719	6,768
Financial instruments	659	1,620
Financial collateral pledged	4,418	2,745
Net amounts	$ 2,642	$ 2,403

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