CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Operating Activities:
Net income	$ 12,993	$ 12,335
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization expense	9,019	7,847
Deferred income taxes	7,171	5,461
Stock-based compensation and other	2,907	3,882
Changes in assets and liabilities	(53,015)	(1,376)
Net cash provided by (used in) operating activities	(20,925)	28,149
Investing Activities:
Capital expenditures	(11,794)	(17,317)
Net cash used in investing activities	(11,794)	(17,317)
Financing Activities:
Net proceeds from issuances of common stock	406	841
Tax benefit of stock-based compensation	49	558
Net cash provided by financing activities	455	1,399
Net increase (decrease) in cash and cash equivalents	(32,264)	12,231
Cash and cash equivalents, beginning of period	259,219	252,415
Cash and cash equivalents, end of period	$ 226,955	$ 264,646