Long-term Debt - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Jan. 11, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Amortization of debt issuance costs (less than $0.1 million)	$ 100,000	$ 100,000
Unamortized debt issuance costs	1,500,000			$ 1,200,000
Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility, maximum borrowing capacity	300,000,000			200,000,000
Revolving credit facility, potential additional borrowing capacity	100,000,000		$ 400,000,000
Basket for permitted stock repurchases				75,000,000
Basket for permitted stock repurchases in any year				20,000,000
Ceiling for dividends allowable				100,000,000
Maximum capacity for acquisitions				$ 150,000,000
Revolving credit facility, remaining balance for stock repurchases	70,100,000
Revolving credit facility, remaining balance for dividends	86,600,000
Revolving credit facility, remaining balance for permitted acquisitions	150,000,000
Revolving credit facility, average borrowings	78,100,000	30,400,000
Minimum amount borrowed at any one time outstanding	10,000,000	10,000,000
Maximum amount borrowed at any one time outstanding	$ 200,000,000	$ 200,000,000
Revolving credit facility, weighted-average interest rate	1.80%	1.70%
Total unused facility fees and letter of credit participation fees	$ 200,000	$ 200,000
Unused facility fee	0.25%
Revolving Credit Facility | Seventh Amendment
Debt Instrument [Line Items]
Revolving credit facility, maximum borrowing capacity			300,000,000
Incurred fees in connection with the Sixth Amendment			$ 300,000
Minimum | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate	1.25%
Maximum | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate	1.75%