Consolidation and Nature of Operations (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash paid during the period for:
Income taxes, net of refunds	$ 2,062	$ 2,503
Interest, net of amounts capitalized	94,870	89,109
Significant non-cash investing and financing activities:
Accrued capital expenditures	80,517	55,286
Dividends declared but not yet paid	$ 73,113	$ 69,484