Derivative Liabilities and Collateral Pledged (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Gross amounts of recognized liabilities	$ 121,394	$ 85,061
Derivative liabilities not subject to master netting agreements	24,200	15,200
Subject to Master Netting Agreements | Derivatives, Interest Rate Contracts
Derivative [Line Items]
Gross amounts of recognized liabilities	97,173	69,842
Gross amounts offset in the Statement of Condition	0	0
Net amounts of liabilities presented in the Statement of Condition	97,173	69,842
Derivative assets available for offset	(11,477)	(17,278)
Collateral pledged	(65,927)	(51,801)
Net amount	$ 19,769	$ 763