CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Operating Activities:
Net income	$ 30,344	$ 35,881
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization expense	21,106	20,258
Deferred income taxes	4,978	13,693
Stock-based compensation and other	2,860	3,173
Changes in assets and liabilities	50,642	(80,453)
Net cash provided by (used in) operating activities	109,930	(7,448)
Investing Activities:
Capital expenditures	(16,163)	(19,833)
Proceeds from disposition of property	10,000	0
Purchase price adjustment	0	4,000
Net cash provided by (used in) investing activities	(6,163)	(15,833)
Financing Activities:
Principal payments on long-term debt	(4,486)	(3,750)
Net proceeds from issuances of common stock	721	3,786
Tax benefit of stock-based compensation	178	1,612
Net cash provided by (used in) financing activities	(3,587)	1,648
Net increase (decrease) in cash and cash equivalents	100,180	(21,633)
Cash and cash equivalents, beginning of period	265,837	232,324
Cash and cash equivalents, end of period	$ 366,017	$ 210,691