Long-term Debt - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	May. 21, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Amortization of debt issuance costs		$ 100,000	$ 100,000	$ 200,000	$ 200,000
Unamortized debt issuance costs	$ 1,200,000	1,200,000		1,200,000			$ 1,100,000
Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility, maximum borrowing capacity	200,000,000	200,000,000		200,000,000
Revolving credit facility, potential additional borrowing capacity	$ 100,000,000	100,000,000		100,000,000
Unused facility fee	25.00%
Revolving credit facility, permitted aggregate stock repurchases	$ 75,000,000	75,000,000		75,000,000
Revolving credit facility, maximum permitted stock repurchases in any year	20,000,000	20,000,000		20,000,000
Revolving credit facility, ceiling for dividends	100,000,000	100,000,000		100,000,000
Revolving credit facility, maximum capacity for acquisitions	150,000,000	150,000,000		150,000,000
Revolving credit facility, remaining balance for stock repurchases	75,000,000	75,000,000		75,000,000
Revolving credit facility, remaining balance for dividends	97,000,000	97,000,000		97,000,000
Revolving credit facility, remaining balance for permitted acquisitions	$ 150,000,000	150,000,000		150,000,000
Incurred fees in connection with the Sixth Amendment						$ 300,000
Revolving credit facility, average borrowings		37,000,000	6,900,000	33,700,000	10,200,000
Minimum amount borrowed at any one time outstanding		0	0	0	0
Maximum amount borrowed at any one time outstanding		$ 120,900,000	$ 46,300,000	$ 120,900,000	$ 46,300,000
Revolving credit facility, weighted-average interest rate		1.80%	1.70%	1.70%	1.60%
Total unused facility fees and letter of credit participation fees		$ 100,000	$ 200,000	$ 300,000	$ 400,000
Revolving Credit Facility | Minimum
Debt Instrument [Line Items]
Revolving credit facility, margin added to variable interest rate				1.25%
Revolving Credit Facility | Maximum
Debt Instrument [Line Items]
Revolving credit facility, margin added to variable interest rate				1.75%