Long-term Debt - Narrative (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Amortization of debt issuance costs	$ 300,000	$ 400,000	$ 400,000
Unamortized debt issuance costs	1,100,000	1,400,000
Revolving credit facility [Member]
Debt Instrument [Line Items]
Revolving credit facility maximum borrowing capacity	200,000,000
Revolving credit facility, potentially additional borrowing capacity	100,000,000
Revolving credit facility, permitted aggregate stock repurchases	50,000,000
Revolving credit facility, maximum permitted stock repurchases in any year	15,000,000
Revolving credit facility, ceiling for dividends	75,000,000
Revolving credit facility, maximum capacity for permitted acquisitions	125,000,000
Revolving credit facility, remaining balance for stock repurchases	38,700,000
Revolving credit facility, remaining balance for dividends	57,400,000
Revolving credit facility, remaining balance for permitted acquisitions	125,000,000
Revolving credit facility, average borrowings	14,800,000	35,300,000
Revolving credit facility, minimum amount borrowed	0	0
Revolving credit facility, maximum amount borrowed	80,300,000	112,000,000
Revolving credit facility, weighted-average interest rate	1.60%	1.80%
Total unused facility fees and letter of credit participation fees	$ 700,000	$ 800,000	$ 900,000
Revolving credit facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Revolving credit facility, margin added to variable interest rate	1.25%
Revolving credit facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Revolving credit facility, margin added to variable interest rate	1.75%