Securities Purchased Under Agreements To Resell And Collateral Pledged By Counterparties (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Securities Purchased under Agreements to Resell [Abstract]
Gross amounts of recognized assets	$ 835,222	$ 613,682
Gross amounts offset in the Statement of Condition	0	0
Net amounts of assets presented in the Statement of Condition	835,222	613,682
Offsetting securities sold under agreements to repurchase	(150)	(1,628)
Securities collateral (not recognized on FHN's Statement of Condition)	(828,596)	(603,813)
Net amount	$ 6,476	$ 8,241