CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues	$ 558,962		$ 533,806		$ 523,118		$ 572,022		$ 545,886		$ 556,053		$ 447,235		$ 434,962		$ 2,187,908	$ 1,984,136	$ 1,731,244
Cost of revenues (exclusive of items shown separately below)	399,743	[1]	372,940	[1]	367,623	[1]	400,315	[1]	373,142	[2]	386,518	[2]	307,754	[2]	312,577	[2]	1,540,621	1,379,991	1,210,740
Selling, general and administrative expenses																	273,520	254,137	205,812
Accretion of environmental liabilities																	9,917	9,680	10,307
Depreciation and amortization																	161,646	122,663	92,473
Income from operations	36,231		56,739		47,533		61,701		59,247		66,792		51,884		39,742		202,204	217,665	211,912
Other (expense) income	(337)		(91)		(75)		(299)		471		164		2,868		2,899		(802)	6,402	2,795
Loss on early extinguishment of debt																	(26,385)	0	(2,294)
Interest expense, net of interest income of $846, $798, and $874, respectively																	(47,287)	(39,389)	(27,936)
Income from continuing operations before provision for income taxes																	127,730	184,678	184,477
(Benefit) provision for income taxes																	(1,944)	57,426	56,756
Income from continuing operations																	129,674	127,252	127,721
Income from discontinued operations, net of tax																	0	0	2,794
Net income	$ 61,874		$ 12,359		$ 23,426		$ 32,015		$ 38,233		$ 37,133		$ 29,156		$ 22,730		$ 129,674	$ 127,252	$ 130,515
Earnings per share:
Basic	$ 1.11		$ 0.23		$ 0.44		$ 0.6		$ 0.72		$ 0.70		$ 0.55		$ 0.43		$ 2.41	$ 2.40	$ 2.48
Diluted	$ 1.11		$ 0.23		$ 0.44		$ 0.6		$ 0.72		$ 0.70		$ 0.55		$ 0.43		$ 2.40	$ 2.39	$ 2.47
Weighted average common shares outstanding																	53,884	52,961	52,622
Weighted average common shares outstanding plus potentially dilutive common shares																	54,079	53,324	52,932

[1] Items shown separately on the statements of income consist of (i) accretion of environmental liabilities and (ii) depreciation and amortization.

[2] The third quarter net income and earnings per share were impacted by a $26.4 million loss on early extinguishment of debt in connection with a redemption and repurchase of our $520.0 million previously outstanding senior secured notes. The fourth quarter 2012 net income and earnings per share were impacted by a decrease in unrecognized tax benefits of $52.4 million resulting from expiring statute of limitation periods related to an historical Canadian debt restructuring transaction.