Derivative Instruments and Hedging Activities - Cash Flow Hedges (Details) - Cash Flow Hedging - USD ($) $ in Thousands		6 Months Ended	12 Months Ended
		Jun. 30, 2019	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gross notional amount outstanding		$ 2,030,000	$ 2,280,000
Derivative asset fair value in other assets	[1]	2,008	6,889
Derivative liability fair value in other liabilities	[1]	$ (1,819)	$ (11,328)
Weighted-average interest rate received		2.13%	2.12%
Weighted-average interest rate paid		2.22%	2.20%
Weighted-average maturity (in years)		1 year 3 months 7 days	1 year 6 months 10 days

[1] Certain cash flow hedges are transacted through a clearinghouse ("centrally cleared") and their change in fair value is settled by the counterparties to the transaction, which results in no fair value.