Derivative Instruments and Hedging Activities - Activity of Derivative Instruments Not Designated as Hedges (Details) - Trading - Interest rate swaps - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Derivative Instruments and Hedging Activities Disclosures [Roll Forward]
Beginning balance	$ 495,500	$ 345,500
Additions	0	50,000
Settlement, Expiration or Exercise	0	0
Ending balance	$ 495,500	$ 395,500