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	27,121			25,229		1,892
Contributions from non-controlling interest holders	11					11
Distributions to non-controlling interest holders	(2,083)					(2,083)
Share-based compensation expense	(184)		(184)
Exercise of stock options	1,977			(4,364)	6,341
Repurchase of shares	(16,781)				(16,781)
Balance at Mar. 31, 2012	176,004	25,413	83,045	147,026	(82,488)	3,008
Balance (in shares) at Mar. 31, 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	28,527			27,518		1,009
Contributions from non-controlling interest holders	12					12
Distributions to non-controlling interest holders	(1,090)					(1,090)
Share-based compensation expense	1,424		1,424
Exercise of stock options	456			(204)	660
Repurchase of shares	(21,997)				(21,997)
Balance at Mar. 31, 2013	$ 167,161	$ 25,413	$ 88,297	$ 151,441	$ (99,291)	$ 1,301
Balance (in shares) at Mar. 31, 2013		25,413