Commitments and Contingent Liabilities - Changes in Allowance for Indemnifications Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in the allowance for indemnification losses
Provision for indemnifications	$ 52	$ 186	$ 290
Indemnification reserve for recourse provisions
Change in the allowance for indemnification losses
Allowance, beginning of period	2,489	2,303
Provision for indemnifications	52	186
Allowance, end of period	$ 2,541	$ 2,489	$ 2,303