CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Trade accounts receivable-billed, allowance	$ 4,149	$ 3,080
Property and equipment, accumulated depreciation	123,126	122,866
Current portion of long-term debt, unamortized discounts	0	296
Long-term debt, unamortized discounts	$ 18,264	$ 23,007
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares reserved for employee stock purchase plan and stock incentive plans	2,702,000	3,971,000
Common stock, shares outstanding	33,516,000	32,261,000
Common stock warrants, vested	439,000	1,426,000
Common stock warrants, issued	1,425,000	2,851,000
Treasury stock, shares	34,075,000	34,919,000
Software
Accumulated amortization	$ 108,986	$ 99,316
Client contracts
Accumulated amortization	$ 97,109	$ 96,723