Financial Instruments Foreign Assets and Liabilites (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Concentration of net assets outside of the U.S.
Cash and cash equivalents	$ 86,655	$ 93,699	$ 74,216	$ 58,096
Other current assets	17,264	14,297
Total assets	5,210,307	5,376,817
Current liabilities	637,157	$ 766,561
Subsidiaries [Member] | CANADA
Concentration of net assets outside of the U.S.
Cash and cash equivalents	17,107
Other current assets	78,542
Noncurrent assets	590,714
Total assets	686,363
Current liabilities	69,798
Noncurrent liabilities	76,192
Total liabilities	145,990
Net assets	$ 540,373