Derivative Instruments and Hedging Activities - Cash Flow Hedges (Details) - Cash Flow Hedging - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gross notional amount outstanding		$ 2,280,000	$ 1,960,000
Derivative asset fair value in other assets	[1]	6,889	3,989
Derivative liability fair value in other liabilities	[1]	$ (11,328)	$ (10,219)
Weighted-average interest rate received		2.12%	1.58%
Weighted-average interest rate paid		2.20%	1.61%
Weighted-average maturity (in years)		1 year 6 months 10 days	2 years 2 months 30 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.