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
Numerator:
Net income attributable to controlling interest	$ 6,852	$ 7,723	$ 29,463	$ 31,953
Denominator:
Denominator for basic earnings per share (in shares)	22,691	22,599	22,675	22,580
Effect of dilutive securities:
Employee stock options and restricted stock units (in shares)	252	306	266	292
Supplemental Executive Retirement Plan (in shares)	110	102	108	101
Denominator for diluted earnings per share (in shares)	23,053	23,007	23,049	22,973
Net income attributable to controlling interest per share:
Basic (in dollars per share)	$ 0.30	$ 0.34	$ 1.30	$ 1.42
Diluted (in dollars per share)	$ 0.30	$ 0.34	$ 1.28	$ 1.39
Antidilutive options (in shares)	1,072	1,072	822	822