Financial Instruments and Concentrations of Risk (Details 5) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 80,029	$ 73,613	$ 87,821	$ 38,192
Other current assets	18,516	28,396
Total assets	1,748,179	1,491,181
Current liabilities	374,344	296,511
Outside Of United States [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	63,002
Other current assets	137,788
Noncurrent assets	389,562
Total assets	590,352
Current liabilities	75,175
Noncurrent liabilities	111,361
Total liabilities	186,536
Net assets	403,816
Canada [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	54,518
Other current assets	92,851
Noncurrent assets	174,171
Total assets	321,540
Current liabilities	51,090
Noncurrent liabilities	81,658
Total liabilities	132,748
Net assets	188,792
United Kingdom [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	3,064
Other current assets	2,780
Noncurrent assets	168,374
Total assets	174,218
Current liabilities	998
Noncurrent liabilities	27,257
Total liabilities	28,255
Net assets	145,963
Mexico [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	5,420
Other current assets	42,157
Noncurrent assets	47,017
Total assets	94,594
Current liabilities	23,087
Noncurrent liabilities	2,446
Total liabilities	25,533
Net assets	$ 69,061