Derivative Instruments - Offsetting of Derivative Assets and Liabilities in the Condensed Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Derivative assets
Gross amounts of recognized assets	$ 25,700	$ 60,105
Gross amounts offset in the statement of financial position	0	(2,440)
Net amounts of assets presented in the statement of financial position	25,700	57,665
Gross amounts of financial instruments not offset in the statement of financial position	0	0
Net amount	25,700	57,665
Derivative liabilities
Gross amounts of recognized liabilities	0	2,440
Gross amounts offset in the statement of financial position	0	(2,440)
Net amounts of liabilities presented in the statement of financial position	0	0
Gross amounts of financial instruments not offset in the statement of financial position	0	0
Net amount	$ 0	$ 0