Consolidation and Nature of Operations (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash paid during the period for:
Income taxes, net of refunds	$ 10,032	$ 2,062
Interest, net of amounts capitalized	104,249	94,870
Significant non-cash investing and financing activities:
Accrued capital expenditures	65,995	80,517
Dividends declared but not yet paid	$ 77,821	$ 73,113