Long-Term Debt and Loan Agreements - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jan. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	May 30, 2014
Debt Instrument [Line Items]
Maximum borrowing capacity on line of credit					$ 300,000,000
Letters of credit		$ 4,400,000
Long-term Debt		190,686,000	$ 193,512,000
Proceeds from issuance of long-term debt		0	0	$ 89,000,000
Long-term debt, excluding unamortized deferred financing costs		189,522,000	191,881,000
Less unamortized deferred financing fees		1,164,000	1,631,000
Senior Unsecured Note [Member]
Debt Instrument [Line Items]
Long-term Debt		100,000,000
4.67% Senior Unsecured Notes due 2021 [Member]
Debt Instrument [Line Items]
Long-term Debt		$ 40,000,000	40,000,000
Interest rate		4.67%
5.25% Senior Unsecured Notes due 2024 [Member]
Debt Instrument [Line Items]
Long-term Debt		$ 11,000,000	11,000,000
Proceeds from issuance of long-term debt		$ 11,000,000
Interest rate		5.25%
Senior Unsecured Notes Excluding 5.25% Senior Unsecured Notes due in 2024 [Member]
Debt Instrument [Line Items]
Proceeds from issuance of long-term debt	$ 89,000,000
5.45% Senior Unsecured Notes due 2026 [Member]
Debt Instrument [Line Items]
Long-term Debt		$ 20,000,000	$ 20,000,000
Interest rate		5.45%
Loan Amendment [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity on line of credit					$ 300,000,000
Remaining amount available under the line of credit		$ 204,900,000
Interest rate during period		4.69%	4.59%