CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Operating Activities:
Net income	$ 13,812	$ 19,602
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization expense	10,471	9,824
Deferred income taxes	796	7,073
Stock-based compensation and other	932	1,270
Changes in assets and liabilities	59,460	(63,584)
Net cash provided by (used in) operating activities	85,471	(25,815)
Investing Activities:
Capital expenditures	(8,443)	(8,397)
Proceeds from disposition of property	10,000	0
Net cash provided by (used in) investing activities	1,557	(8,397)
Financing Activities:
Principal payments on long-term debt	(2,611)	(1,875)
Net proceeds from issuances of common stock	399	2,201
Tax benefit of stock-based compensation	147	946
Net cash provided by (used in) financing activities	(2,065)	1,272
Net increase (decrease) in cash and cash equivalents	84,963	(32,940)
Cash and cash equivalents, beginning of period	265,837	232,324
Cash and cash equivalents, end of period	$ 350,800	$ 199,384