Depreciation and Interest Charges on Property, Plant and Equipment (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Property Plant And Equipment [Abstract]
Depreciation and amortization on PP&E	$ 14.6us-gaap_Depreciation	$ 14.7us-gaap_Depreciation
Interest charges capitalized (in construction in progress)	$ 0.3us-gaap_InterestCostsCapitalized	$ 0.2us-gaap_InterestCostsCapitalized

Amount of interest capitalized during the period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Allowance for Funds Used during Construction

-URI http://asc.fasb.org/extlink&oid=6504829

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391

Name:	us-gaap_InterestCostsCapitalized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration