Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Trust Assets) $ in Thousands	Dec. 31, 2017 USD ($) trust_accounts	Dec. 31, 2016 USD ($) trust_accounts
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of Trust Accounts managed or administered | trust_accounts	1,119	1,231
Value of Trust Accounts | $	$ 997,790	$ 831,600