Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Consolidated Balance Sheets [Abstract]
Accounts receivable, allowances	$ 358	$ 263
Property and equipment, accumulated depreciation	$ 152,206	$ 125,798
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	75,000,000	75,000,000
Common stock, shares issued	36,855,466	36,413,611
Common stock, shares outstanding	29,655,466	32,913,611
Treasury stock, shares	7,200,000	3,500,000