CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Operating Activities:
Net income	$ 51,544	$ 51,432
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization expense	31,728	31,024
Deferred income taxes	11,148	20,214
Stock-based compensation and other	1,753	3,381
Changes in assets and liabilities	84,256	(74,259)
Net cash provided by (used in) operating activities	180,429	31,792
Investing Activities:
Capital expenditures	(24,784)	(27,529)
Proceeds from disposition of property	10,000	0
Purchase price adjustment	0	4,000
Net cash provided by (used in) investing activities	(14,784)	(23,529)
Financing Activities:
Principal payments on long-term debt	(6,361)	(5,625)
Net proceeds from issuances of common stock	965	4,131
Tax benefit of stock-based compensation	1,412	2,218
Net cash provided by (used in) financing activities	(3,984)	724
Net increase (decrease) in cash and cash equivalents	161,661	8,987
Cash and cash equivalents, beginning of period	265,837	232,324
Cash and cash equivalents, end of period	$ 427,498	$ 241,311