CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (USD $) In Thousands, except Share data	Total	Common Class A [Member]	Common Class B [Member]	Additional Paid In Capital [Member]	Retained Earnings [Member]
Opening Balance VALUE at Dec. 31, 2011	$ 248,911	$ 310	$ 72	$ 597,327	$ (348,798)
Opening Balance SHARES at Dec. 31, 2011		31,044,001	7,197,532
Conversion of Class B common stock to Class A common stock SHARES		0	0
Compensation expense related to granting of stock options SHARES		0	0
Compensation expense related to granting of restricted stock units SHARES		280,072	0
Issuance of common stock related to an incentive plan SHARES		0	0
Common stock repurchase SHARES		0	0
Exercise of stock options SHARES		101,350	0
Purchase of vested employee restricted stock units SHARES		(199,376)	0
Net income (loss)	11,268	0	0	0	11,268
Conversion of Class B common stock to Class A common stock VALUE	0	0	0	0	0
Compensation expense related to granting of stock options VALUE	210	0	0	210	0
Compensation expense related to granting of restricted stock units VALUE	5,544	3	0	5,541	0
Issuance of common stock related to an incentive plan VALUE	0	0	0	0	0
Common stock repurchase VALUE	0	0	0	0	0
Purchase of vested employee restricted stock units	(1,367)	(2)	0	(1,365)	0
Forfeitures of dividend equivalents VALUE	16	0	0	0	16
Realization of tax benefit for dividend equivalent payments VALUE	0	0	0	0	0
Exercise of stock options VALUE	135	1	0	134	0
Net unrealized gain (loss) on derivatives VALUE	0	0	0	0	0
Ending Balance VALUE at Dec. 31, 2012	264,717	312	72	601,847	(337,514)
Ending Balance SHARES at Dec. 31, 2012		31,226,047	7,197,532
Conversion of Class B common stock to Class A common stock SHARES		0	0
Compensation expense related to granting of stock options SHARES	5,000	0	0
Compensation expense related to granting of restricted stock units SHARES		298,270	0
Issuance of common stock related to an incentive plan SHARES		0	0
Common stock repurchase SHARES		0	0
Exercise of stock options SHARES	(153,782)	153,782	0
Purchase of vested employee restricted stock units SHARES		(138,676)	0
Net income (loss)	16,517	0	0	0	16,517
Conversion of Class B common stock to Class A common stock VALUE	0	0	0	0	0
Compensation expense related to granting of stock options VALUE	37	0	0	37	0
Compensation expense related to granting of restricted stock units VALUE	2,943	3	0	2,940	0
Issuance of common stock related to an incentive plan VALUE	0	0	0	0	0
Common stock repurchase VALUE	0	0	0	0	0
Purchase of vested employee restricted stock units	(1,167)	(1)	0	(1,166)	0
Payments of dividends VALUE	0	0	0	0	0
Forfeitures of dividend equivalents VALUE	0	0	0	0	0
Exercise of stock options VALUE	219	1	0	218	0
Net unrealized gain (loss) on investments VALUE	0	0	0	0	0
Net unrealized gain (loss) on derivatives VALUE	0	0	0	0	0
Ending Balance VALUE at Sep. 30, 2013	$ 283,266	$ 315	$ 72	$ 603,876	$ (320,997)
Ending Balance SHARES at Sep. 30, 2013		31,539,423	7,197,532