Interest (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Summarized of interest incurred, capitalized and paid as well as the amortization of capitalized interest
Interest incurred	$ 3,012	$ 3,286	$ 3,334
Less capitalized interest	225	250	200
Total net expense	2,787	3,036	3,134
Interest paid	2,215	2,671	2,639
Amortization of capitalized interest included in cost of sales	$ 261	$ 265	$ 336