Fair Value of Financial Instruments - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Fair Value, Option, Quantitative Disclosures [Line Items]
Federal home loan bank and federal reserve stock required to be owned by company	$ 400.0		$ 403.0
Forward contracts
Fair Value, Option, Quantitative Disclosures [Line Items]
Net gains (losses) realized due to changes in fair value of loans	(2.7)	$ (1.5)
Noninterest income | Residential mortgage loans held for sale
Fair Value, Option, Quantitative Disclosures [Line Items]
Net gains (losses) realized due to changes in fair value of loans	$ 1.3	$ 1.9