Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Accounts receivable, allowance	$ 851	$ 973
Accumulated depreciation	98,705	83,404
Accumulated amortization	$ 81,198	$ 77,622
Common Stock, par value
Common Stock, shares authorized	55,000,000	55,000,000
Common Stock, shares issued	33,856,629	36,761,362
Common Stock, shares outstanding	33,856,629	36,761,362