CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Property and equipment, accumulated depreciation	$ 101,446	$ 95,472
Intangible assets, accumulated amortization	$ 36,799	$ 33,050
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)	36,599,273	36,252,280
Common stock, outstanding (shares)	32,246,575	31,973,505
Treasury stock at cost (shares)	4,352,698	4,278,775

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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Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.

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