Condensed Consolidated Statements of Changes in Shareholders’ Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock	Common Stock Subscribed, Unissued	Retained Earnings	Accumulated Other Comprehensive Loss	Noncontrolling Interests
Balance at Dec. 31, 2010	$ 558,807	$ 232,400	$ 0	$ 423,602	$ (102,343)	$ 5,148
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Net income	68,340			67,995		345
Other comprehensive income	5,239				5,318	(79)
Stock issued	9,878	9,366				512
Stock purchased	(7,444)	(7,340)				(104)
Advance payments	379		379
Dividends declared	(10,572)			(10,572)
Balance at Sep. 30, 2011	624,627	234,426	379	481,025	(97,025)	5,822
Balance at Dec. 31, 2011	571,394	257,630	0	458,139	(150,364)	5,989
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Net income	79,366			79,155		211
Other comprehensive income	12,939				13,084	(145)
Stock issued	10,106	10,106
Stock purchased	(10,974)	(8,119)				(2,855)
Advance payments	395		395
Dividends declared	(11,729)			(11,729)
Balance at Sep. 30, 2012	$ 651,497	$ 259,617	$ 395	$ 525,565	$ (137,280)	$ 3,200