CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Operating Activities:
Net income	$ 51,432	$ 47,059
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization expense	31,024	27,995
Deferred income taxes	20,214	24,109
Stock-based compensation and other	3,381	7,924
Changes in assets and liabilities	(74,259)	(126,414)
Net cash provided by (used in) operating activities	31,792	(19,327)
Investing Activities:
Capital expenditures	(27,529)	(40,801)
Proceeds from disposition of property	0	25,589
Purchase price adjustment	4,000	0
Net cash provided by (used in) investing activities	(23,529)	(15,212)
Financing Activities:
Principal payments on long-term obligations	(5,625)	0
Net proceeds from issuances of common stock	4,131	2,590
Tax benefit of stock-based compensation	2,218	253
Net cash provided by (used in) financing activities	724	2,843
Net increase (decrease) in cash and cash equivalents	8,987	(31,696)
Cash and cash equivalents, beginning of period	232,324	259,219
Cash and cash equivalents, end of period	$ 241,311	$ 227,523