Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Accumulated amortization of intangible assets	$ 21,422	$ 21,133
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Common stock, par value (in dollars per share)	$ 0.025	$ 0.025
Common stock, shares authorized (in shares)	140,000,000	140,000,000
Common stock, shares issued (in shares)	84,245,940	83,962,182
Common stock, shares outstanding (in shares)	84,245,940	83,962,182