Line of Credit (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	May 07, 2014
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 125.0		$ 90.0
Line of Credit Facility Maximum Borrowing Capacity Increase	35.0		15.0
Line of credit facility, commitment increase	50.0	25.0
Line of credit facility, allowable issuance amount of letters of credit	10.0
Letters of credit outstanding	0.2
Credit agreement, final maturity date	Jul. 31, 2017
Line of credit, interest rate at period end (in hundredths)	0.18%
Line of credit facility, percentage of annual commitment fee on unused capacity (in hundredths)	0.20%
Unused portion of line of credit	$ 57.3
Minimum [Member]
Line of Credit Facility [Line Items]
Line of credit, margin interest rate percentage (in hundredths)	2.00%
Ratio of EBITDA plus stock compensation and minus income taxes paid and capital expenditures to interest expense and scheduled payments due for borrowings	1.00
Ratio of current maturities of long-term debt to EBITDA plus stock compensation and minus income taxes paid and capital expenditures	1.00
Maximum [Member]
Line of Credit Facility [Line Items]
Line of credit, margin interest rate percentage (in hundredths)	2.50%
Ratio of EBITDA plus stock compensation and minus income taxes paid and capital expenditures to interest expense and scheduled payments due for borrowings	2.00
Ratio of current maturities of long-term debt to EBITDA plus stock compensation and minus income taxes paid and capital expenditures	2.75
Silicon Valley Bank [Member]
Line of Credit Facility [Line Items]
Line of credit, interest rate at period end (in hundredths)	4.00%
Silicon Valley Bank [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Line of credit, margin interest rate percentage (in hundredths)	0.00%
Silicon Valley Bank [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Line of credit, margin interest rate percentage (in hundredths)	0.50%