CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Allowance for doubtful accounts receivable (in dollars)	$ 1,912	$ 1,581
Accumulated depreciation (in dollars)	$ 124,884	$ 115,792
Preferred stock, shares issued	0	0
Shares to be issued, shares	28,000	28,000
Common Class A [Member]
Common stock, shares issued	31,465,723	31,074,168
Common stock, shares outstanding	31,465,723	31,074,168
Common Class B [Member]
Common stock, shares issued	2,503	2,503
Common stock, shares outstanding	2,503	2,503