Securities Purchased Under Agreements To Resell And Collateral Pledged By Counterparties (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Securities Purchased under Agreements to Resell [Abstract]
Gross amounts of recognized assets	$ 910,670	$ 725,609
Gross amounts offset in the Statements of Condition	0	0
Net amounts of assets presented in the Statements of Condition	910,670	725,609
Offsetting securities sold under agreements to repurchase	(365)	(259)
Securities collateral (not recognized on FHN’s Statements of Condition)	(903,580)	(720,036)
Net amount	$ 6,725	$ 5,314