Balance Sheet Offsetting (Details) - September 30, 2018 - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Offsetting Derivative Assets [Abstract]
Gross amounts recognized	$ 78,124	$ 29,503
Gross amounts offset in the balance sheet	0	0
Net amounts presented in the balance sheet	78,124	29,503
Financial instruments	(26,385)	(16,140)
Collateral	(50,134)	(13,234)
Net amount	1,605	129
Offsetting Derivative Liabilities [Abstract]
Gross amounts recognized	64,591	37,164
Gross amounts offset in the balance sheet	0	0
Net amounts presented in the balance sheet	64,591	37,164
Financial instruments	(26,385)	(16,140)
Collateral	(37,480)	(20,662)
Net amount	$ 726	$ 362

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