Derivative Instruments and Hedging Activities - Offsetting Derivatives (Details) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Assets
Gross amounts recognized		$ 35,080	$ 21,068
Less: amounts offset in the Consolidated Statements of Financial Condition		0	0
Net amount presented in the Consolidated Statements of Financial Condition	[1]	35,080	21,068
Offsetting derivative positions		(14,704)	(16,880)
Cash collateral pledged		(17,360)	0
Net credit exposure		3,016	4,188
Liabilities
Gross amounts recognized		48,040	25,250
Less: amounts offset in the Consolidated Statements of Financial Condition		0	0
Net amount presented in the Consolidated Statements of Financial Condition	[1]	48,040	25,250
Offsetting derivative positions		(14,704)	(16,880)
Cash collateral pledged		(4,480)	(8,370)
Net credit exposure		$ 28,856	$ 0

[1] Included in other assets or other liabilities in the Consolidated Statements of Financial Condition.