SIGNIFICANT ACCOUNTING POLICIES Supplementary Cash Flows Information (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplementary cash flows information:
Interest paid (net of interest capitalized)		$ 191,041	$ 185,288	$ 155,112
Income taxes paid — net		55,722	44,524	20,092
Supplementary non-cash investing and financing activities:
Additions to property, plant and equipment and other long-lived assets	[1]	110,354	90,949	68,276
Allowance for equity funds used during construction		$ 28,075	$ 20,825	$ 30,159

[1] Amounts consist of current liabilities for construction labor and materials that have not been included in investing activities. These amounts have not been paid for as of December 31, 2015, 2014 or 2013, respectively, but have been or will be included as a cash outflow from investing activities for expenditures for property, plant and equipment when paid.