Related Party Transactions (Ending balances of, and contributions to the Isabella Bank Foundation) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Summary of assets and contribution made to entity
Ending assets	$ 1,493,137	$ 1,430,639
Isabella Bank Foundation [Member]
Summary of assets and contribution made to entity
Ending assets	1,815	1,766	1,150
Donations	$ 200	$ 850	$ 250