Line Of Credit (Details) (USD $)	9 Months Ended
	Sep. 30, 2013
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 75,000,000
Line of credit facility, commitment increase	25,000,000
Line of credit facility, allowable issuance amount of letters of credit	5,000,000
Line of Credit Facility Allowable Amount for Swingline Loans	10,000,000
Letters of credit outstanding	200,000
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)	0.30%
Unused portion of line of credit	$ 58,800,000
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%