Assets Manufactured for Internal Use (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Assets manufactured for internal use
Cost	$ 87,206,000	$ 86,527,000
Accumulated depreciation	(55,200,000)	(52,114,000)
Net	32,006,000	34,413,000
Depreciation expense	3,200,000	3,300,000	3,500,000
Assets Manufactured for Internal Use
Assets manufactured for internal use
Cost	28,672,000	23,727,000
Accumulated depreciation	(15,774,000)	(13,948,000)
Net	12,898,000	9,779,000
Depreciation expense	1,800,000	3,400,000	4,900,000
Assets Manufactured for Internal Use | Internal use assets
Assets manufactured for internal use
Cost	23,409,000	21,904,000
Assets Manufactured for Internal Use | Construction in process
Assets manufactured for internal use
Cost	$ 5,263,000	$ 1,823,000