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	56,473			53,310		3,163
Contributions from non-controlling interest holders	24					24
Distributions to non-controlling interest holders	(4,830)					(4,830)
Share-based compensation expense	892		892
Exercise of stock options	2,018			(4,397)	6,415
Repurchase of shares	(16,781)				(16,781)
Balance at Jun. 30, 2012	203,739	25,413	84,121	175,074	(82,414)	1,545
Balance (in shares) at Jun. 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	60,595			58,449		2,146
Contributions from non-controlling interest holders	15					15
Distributions to non-controlling interest holders	(1,889)					(1,889)
Share-based compensation expense	1,519		1,519
Exercise of stock options	2,914			(3,639)	6,553
Repurchase of shares	(51,573)				(51,573)
Balance at Jun. 30, 2013	$ 171,410	$ 25,413	$ 88,392	$ 178,937	$ (122,974)	$ 1,642
Balance (in shares) at Jun. 30, 2013		25,413