Fair Value (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Summary of changes in fair value of marketable securities [Roll Forward]
Balance, beginning of period	$ 23,172,000	$ 18,605,000
Actual return on plan assets: [Abstract]
Relating to assets still held at the reporting date	1,249,000	2,568,000
Purchases and issuances	2,798,000	3,408,000
Sales and settlements	(939,000)	(1,409,000)
Transfers into Level 3	0	0
Balance, End of period	26,280,000	23,172,000
Fair Value on a Recurring Basis [Member]
Financial assets (liabilities) [Abstract]
Cash equivalents and current investments	86,574,000	61,136,000
Forward contracts	1,661,000	1,939,000
Insurance company contracts	26,280,000	23,172,000
Total	114,515,000	86,247,000
Restricted current investments	11,800	22,000
Fair Value on a Recurring Basis [Member] | Level 1 [Member]
Financial assets (liabilities) [Abstract]
Cash equivalents and current investments	86,574,000	61,136,000
Forward contracts	0	0
Insurance company contracts	0	0
Total	86,574,000	61,136,000
Fair Value on a Recurring Basis [Member] | Level 2 [Member]
Financial assets (liabilities) [Abstract]
Cash equivalents and current investments	0	0
Forward contracts	1,661,000	1,939,000
Insurance company contracts	0	0
Total	1,661,000	1,939,000
Fair Value on a Recurring Basis [Member] | Level 3 [Member]
Financial assets (liabilities) [Abstract]
Cash equivalents and current investments	0	0
Forward contracts	0	0
Insurance company contracts	26,280,000	23,172,000
Total	$ 26,280,000	$ 23,172,000