CONDENSED CONSOLIDATED STATEMENTS OF EQUITY (USD $) In Thousands, unless otherwise specified	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock, at Cost	Non-controlling Interests
Balance at Dec. 31, 2010	$ 151,898	$ 25,413	$ 79,297	$ 58,546	$ (14,418)	$ 3,060
Balance (in shares) at Dec. 31, 2010		25,413
Increase (Decrease) in Stockholders' Equity
Net income	49,776			45,381		4,395
Contributions from non-controlling interest holders	31					31
Distributions to non-controlling interest holders	(5,443)					(5,443)
Share-based compensation expense	2,109		2,109
Exercise of stock options	775			(2,943)	3,718
Repurchase of shares	(35,471)				(35,471)
Balance at Sep. 30, 2011	163,675	25,413	81,406	100,984	(46,171)	2,043
Balance (in shares) at Sep. 30, 2011		25,413
Balance at Dec. 31, 2011	165,943	25,413	83,229	126,161	(72,048)	3,188
Balance (in shares) at Dec. 31, 2011		25,413
Increase (Decrease) in Stockholders' Equity
Net income	84,557			80,334		4,223
Contributions from non-controlling interest holders	27					27
Distributions to non-controlling interest holders	(6,008)					(6,008)
Share-based compensation expense	2,038		2,038
Exercise of stock options	2,619			(5,759)	8,378
Repurchase of shares	(16,781)				(16,781)
Balance at Sep. 30, 2012	$ 232,395	$ 25,413	$ 85,267	$ 200,736	$ (80,451)	$ 1,430
Balance (in shares) at Sep. 30, 2012		25,413