Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Cash Flow Elements [Abstract]
Amount paid for interest	$ 45,472	$ 44,063	$ 54,763
Amount paid for income taxes, net	42,003	132,695	34,404
Non-cash conversion of convertible notes to common shares	0	43,215	44,310
Accrued capital expenditures	$ 13,824	$ 12,391	$ 5,074