Long-term Debt - Narrative (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Debt Instrument [Line Items]
Amortization of debt issuance costs	$ 100,000	$ 100,000	$ 200,000	$ 200,000
Unamortized debt issuance costs	1,300,000		1,300,000		1,400,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Revolving credit facility, maximum borrowing capacity	200,000,000		200,000,000
Revolving credit facility, potentially additional borrowing capacity	100,000,000		100,000,000
Revolving credit facility, permitted aggregate stock repurchases	50,000,000		50,000,000
Revolving credit facility, Maximum permitted stock repurchases in any year	15,000,000		15,000,000
Revolving credit facility, ceiling for dividends	75,000,000		75,000,000
Revolving credit facility, average borrowings	6,900,000	41,400,000	10,200,000	37,900,000
Minimum amount borrowed at any one time outstanding	0	0	0	0
Maximum amount borrowed at any one time outstanding	46,300,000	112,000,000	46,300,000	112,000,000
Revolving credit facility, weighted-average interest rate	1.70%	1.90%	1.60%	2.00%
Total unused facility fees and letter of credit participation fees	$ 200,000	$ 200,000	$ 400,000	$ 500,000
Line of Credit [Member] | Revolving Credit Facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Revolving credit facility, margin added to variable interest rate			1.25%
Line of Credit [Member] | Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Revolving credit facility, margin added to variable interest rate			1.75%