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, 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 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
Balance at Dec. 31, 2012	159,829	25,413	86,873	124,127	(77,954)	1,370
Balance (in shares) at Dec. 31, 2012		25,413
Increase (Decrease) in Equity
Net income	97,550			94,457		3,093
Contributions from non-controlling interest holders	18					18
Distributions to non-controlling interest holders	(3,234)					(3,234)
Share-based compensation expense	2,076		2,076
Exercise of stock options	4,710			(8,801)	13,511
Repurchase of shares	(87,418)				(87,418)
Balance at Sep. 30, 2013	$ 173,531	$ 25,413	$ 88,949	$ 209,783	$ (151,861)	$ 1,247
Balance (in shares) at Sep. 30, 2013		25,413