CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Property and equipment, accumulated depreciation	$ 95,472	$ 146,814
Intangible assets, accumulated amortization	$ 33,050	$ 30,610
Preferred stock, par value (usd per share)	$ 0.001	$ 0.001
Preferred stock, authorized (shares)	5,000,000	5,000,000
Preferred stock, issued (shares)	0	0
Preferred stock, outstanding (shares)	0	0
Common stock, par value (usd per share)	$ 0.001	$ 0.001
Common stock, authorized (shares)	60,000,000	60,000,000
Common stock, issued (shares)	36,252,280	35,747,134
Common stock, outstanding (shares)	31,973,505	33,964,767
Treasury stock at cost (shares)	4,278,775	1,782,367

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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