Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Common Class A [Member]
Numerator:
Allocation of net income	$ 5,465	$ 662	$ 13,478	$ 1,078
Denominator:
Weighted-average shares outstanding	20,041,620	19,976,954	20,026,652	20,005,149
Basic net income per share	$ 0.27	$ 0.03	$ 0.67	$ 0.05
Numerator:
Allocation of net income	5,465	662	13,478	1,078
Denominator:
Number of shares used in basic computation	20,041,620	19,976,954	20,026,652	20,005,149
Weighted-average shares effect of dilutive securities
Add: Director and employee stock options	268,476		310,117
Number of shares used in per share computations	20,310,096	19,976,954	20,336,769	20,005,149
Diluted net income per share	$ 0.27	$ 0.03	$ 0.66	$ 0.05
Common Class B [Member]
Numerator:
Allocation of net income	1,374	158	3,395	254
Denominator:
Weighted-average shares outstanding	5,576,775	5,576,775	5,576,775	5,576,775
Basic net income per share	$ 0.25	$ 0.03	$ 0.61	$ 0.05
Numerator:
Allocation of net income	$ 1,374	$ 158	$ 3,395	$ 254
Denominator:
Number of shares used in basic computation	5,576,775	5,576,775	5,576,775	5,576,775
Weighted-average shares effect of dilutive securities
Number of shares used in per share computations	5,576,775	5,576,775	5,576,775	5,576,775
Diluted net income per share	$ 0.25	$ 0.03	$ 0.61	$ 0.05