Cash Flow Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash paid during the year:
Interest paid, net of amounts capitalized	$ 14,667	$ 18,094	$ 21,966
Non-cash investing activities - capital assets acquired under installment contracts	$ 6,005