Fair Value Measurements (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross unrealized gains associated with the investment held in the rabbi trust	$ 147,000	$ 87,000	$ (251,000)
Fair value of investments	100,000	100,000
Gross unrealized gains	100,000	100,000
Transfers in out between levels	0	0
Carrying amount of long-term debt	232,625,000
Investments held in Rabbi Trust [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of investments	5,800,000
Available-for-sale securities measured at fair value	6,500,000	3,300,000
Investments held in Rabbi Trust [Member] | SERP [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross unrealized gains associated with the investment held in the rabbi trust	700,000	400,000
Fair value of long-term debt	233,300,000
Carrying amount of long-term debt	232,625,000
Available-for-sale securities measured at fair value	$ 6,500,000	$ 3,300,000