Acquisitions (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2015 USD ($)
Other disclosures
Increase in cost of sales for fair value mark-up of acquired inventory	$ 2.0	$ 8.0
Pre-tax acquisition and integration costs	1.6	9.3
Penford And Kerr Acquisitions
Other disclosures
Pre-tax acquisition and integration costs	2.0	9.0
Penford
Other disclosures
Increase in cost of sales for fair value mark-up of acquired inventory		$ 6.0
Penford | Customer Relationships | Minimum
Identifiable intangible assets
Estimated Remaining Useful Life		15 years
Penford | Customer Relationships | Maximum
Identifiable intangible assets
Estimated Remaining Useful Life		22 years
Penford | Trade names | Minimum
Identifiable intangible assets
Estimated Remaining Useful Life		10 years
Penford | Technology | Minimum
Identifiable intangible assets
Estimated Remaining Useful Life		6 years
Penford | Technology | Maximum
Identifiable intangible assets
Estimated Remaining Useful Life		11 years
Penford | Noncompetition Agreements
Identifiable intangible assets
Estimated Remaining Useful Life		2 years
Kerr
Other disclosures
Increase in cost of sales for fair value mark-up of acquired inventory	2.0	$ 2.0
Level 3 | Penford | Customer Relationships | Multi-period excess earnings method
Identifiable intangible assets
Fair Value	84.0	84.0
Level 3 | Penford | Trade names | Relief-from-royalty method
Identifiable intangible assets
Fair Value	17.0	17.0
Level 3 | Penford | Technology | Relief-from-royalty method
Identifiable intangible assets
Fair Value	17.0	17.0
Level 3 | Penford | Noncompetition Agreements | Income Approach
Identifiable intangible assets
Fair Value	$ 3.0	$ 3.0