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	35,649			35,449		200
Other comprehensive income	6,570				6,502	68
Stock issued	6,926	6,926
Stock purchased	(4,551)	(4,488)				(63)
Advance payments	377		377
Dividends declared	(7,053)			(7,053)
Balance at Jun. 30, 2011	596,725	234,838	377	451,998	(95,841)	5,353
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	59,286			59,143		143
Other comprehensive income	6,507				6,750	(243)
Stock issued	7,555	7,555
Stock purchased	(7,544)	(4,736)				(2,808)
Advance payments	768		768
Dividends declared	(7,833)			(7,833)
Balance at Jun. 30, 2012	$ 630,133	$ 260,449	$ 768	$ 509,449	$ (143,614)	$ 3,081