Master Netting and Similar Agreements—Repurchase, Reverse Repurchase, and Securities Borrowing Transactions - Securities Sold Under Agreements To Repurchase And Collateral Pledged By Company (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Offsetting [Abstract]
Gross amounts of recognized liabilities	$ 678,510	$ 656,602
Gross amounts offset in the Statements of Condition	0	0
Net amounts of liabilities presented in the Statements of Condition	678,510	656,602
Gross amounts not offset in the Statements of Condition
Offsetting securities purchased under agreements to resell	(1,017)	(259)
Securities/ government guaranteed loans collateral	(677,125)	(656,216)
Net amount	$ 368	$ 127