Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash paid during the year:
Interest paid, net of amounts capitalized	$ 14,666	$ 13,706	$ 16,178
Non-cash investing activities - capital assets acquired under installment contracts	2,497	1,309	90
Non-cash financing activities - common shares issued for performance based compensation, net of withholding taxes paid	400
Cash and cash equivalents	40,759	15,821
Restricted cash included in other current assets
Escrow deposits for capacity sales		5,000
Restricted cash included in other assets
Other	250	325
Total cash, cash equivalents and restricted cash	$ 41,009	$ 21,146	$ 34,137	$ 40,435