Earnings Per Share - Summary of Reconciliation of Numerators and Denominators Used in Basic and Diluted Per Share Computations (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Class A common stock [Member]
Numerator:
Allocation of net income	$ 1,577	$ 2,102	$ 1,067	$ 7,304
Denominator:
Weighted-average shares outstanding	20,961,526	21,202,571	20,917,529	20,637,801
Basic net income per share	$ 0.08	$ 0.10	$ 0.05	$ 0.35
Numerator:
Allocation of net income	1,577	2,102	1,067	7,304
Denominator:
Number of shares used in basic computation	20,961,526	21,202,571	20,917,529	20,637,801
Weighted-average shares effect of dilutive securities
Add: Director and employee stock options	388,838	401,309	384,512	346,296
Number of shares used in per share computations	21,350,364	21,603,880	21,302,041	20,984,097
Diluted net income per share	$ 0.07	$ 0.10	$ 0.05	$ 0.35
Class B common stock [Member]
Numerator:
Allocation of net income	362	527	237	1,801
Denominator:
Weighted-average shares outstanding	5,576,775	5,576,775	5,576,775	5,576,775
Basic net income per share	$ 0.07	$ 0.09	$ 0.04	$ 0.32
Numerator:
Allocation of net income	$ 362	$ 527	$ 237	$ 1,801
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
Add: Director and employee stock options	0		0
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	$ 0.07	$ 0.09	$ 0.04	$ 0.32