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, 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
Balance at Dec. 31, 2011						5,989
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Stock issued
Balance at Sep. 30, 2012
Balance at Dec. 31, 2012	600,216	310,008	0	453,770	(166,814)	3,252
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Net income	29,905			29,837		68
Other comprehensive income	4,176				4,336	(160)
Stock issued	8,231	8,231
Stock purchased	(7,095)	(7,025)				(70)
Advance payments	805		805
Dividends declared	(9,376)			(9,376)
Balance at Jun. 30, 2013	$ 626,862	$ 311,214	$ 805	$ 474,231	$ (162,478)	$ 3,090