Earnings per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Numerator:
Net income attributable to controlling interest	$ 10,366	$ 14,086	$ 22,611	$ 24,230
Denominator:
Denominator for basic earnings per share (in shares)	22,691	22,576	22,667	22,571
Effect of dilutive securities:
Employee stock options and restricted stock units (in shares)	242	315	274	285
Supplemental Executive Retirement Plan (in shares)	108	101	106	100
Denominator for diluted earnings per share (in shares)	23,041	22,992	23,047	22,956
Net income attributable to controlling interest per share:
Basic (in dollars per share)	$ 0.46	$ 0.62	$ 1.00	$ 1.07
Diluted (in dollars per share)	$ 0.45	$ 0.61	$ 0.98	$ 1.06
Antidilutive options (in shares)	1,072	323	698	698