Debt (Details) (USD $)
3 Months Ended
Mar. 31, 2015
Revolving Credit Facility [Member]  
Line of Credit Facility [Line Items]  
Revolving line of credit borrowing capacity $ 125,000,000.0
Additional borrowing capacity under revolving line of credit facility 25,000,000.0
Amount provided by credit agreement 75,000,000
Remaining amount available under revolving line of credit facility 49,700,000
Percentage of unused commitment fee, per annum 0.25%
Revolving line of credit interest rate, per annum 0.9375%
Revolving Credit Facility [Member] | LIBOR [Member] | Minimum [Member]  
Line of Credit Facility [Line Items]  
Variable interest rate, percentage in addition to base rate 0.75%
Revolving Credit Facility [Member] | LIBOR [Member] | Maximum [Member]  
Line of Credit Facility [Line Items]  
Variable interest rate, percentage in addition to base rate 1.75%
Revolving Credit Facility [Member] | Prime Rate [Member] | Minimum [Member]  
Line of Credit Facility [Line Items]  
Variable interest rate, percentage in addition to base rate 0.00%
Revolving Credit Facility [Member] | Prime Rate [Member] | Maximum [Member]  
Line of Credit Facility [Line Items]  
Variable interest rate, percentage in addition to base rate 0.75%
Letters of Credit [Member]  
Line of Credit Facility [Line Items]  
Amount provided by credit agreement $ 300,000