Borrowings (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)
Line of Credit Facility [Line Items]
Capitalized leases	$ 8,362	$ 8,716
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit Agreement initiation date	Oct. 10, 2014
Credit Agreement aggregate principal amount	$ 150,000
Credit Agreement term	5 years
Credit Agreement optional increase in aggregate principal amount	$ 75,000
Credit Agreement maturity date	Oct. 10, 2019
Credit Agreement maximum consolidated total leverage ratio	3.00
Credit Agreement minimum interest coverage ratio	3.50
Credit Agreement availability	$ 150,000
Credit Agreement maximum cash dividends in a fiscal year	30,000
Credit Agreement outstanding balance	$ 0	$ 0
Revolving Credit Facility [Member] | Federal Funds Open Rate [Member]
Line of Credit Facility [Line Items]
Credit Agreement applicable margin	0.50%
Revolving Credit Facility [Member] | LIBOR Rate [Member]
Line of Credit Facility [Line Items]
Credit Agreement applicable margin	1.00%
Minimum [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit Agreement quarterly commitment fee percentage	0.20%
Minimum [Member] | Revolving Credit Facility [Member] | Leverage Ratio [Member]
Line of Credit Facility [Line Items]
Credit Agreement applicable margin	0.25%
Minimum [Member] | Revolving Credit Facility [Member] | LIBOR Rate Plus Levarage Ratio [Member]
Line of Credit Facility [Line Items]
Credit Agreement applicable margin	1.25%
Maximum [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit Agreement quarterly commitment fee percentage	0.25%
Maximum [Member] | Revolving Credit Facility [Member] | Leverage Ratio [Member]
Line of Credit Facility [Line Items]
Credit Agreement applicable margin	0.50%
Maximum [Member] | Revolving Credit Facility [Member] | LIBOR Rate Plus Levarage Ratio [Member]
Line of Credit Facility [Line Items]
Credit Agreement applicable margin	1.50%