CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Property and equipment, accumulated depreciation	$ 96,892	$ 95,472
Intangible assets, accumulated amortization	$ 33,166	$ 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)	36,337,743	36,252,280
Common stock, outstanding (shares)	32,037,667	31,973,505
Treasury stock at cost (shares)	4,300,076	4,278,775