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, 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
Balance at Dec. 31, 2013	670,781	317,767	0	489,740	(140,363)	3,637
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Net income	40,457			40,365		92
Other comprehensive income	5,699				5,715	(16)
Stock issued	9,211	9,211
Stock purchased	(10,592)	(10,306)				(286)
Advance payments	860		860
Dividends declared	(9,548)			(9,548)
Balance at Jun. 30, 2014	$ 706,868	$ 316,672	$ 860	$ 520,557	$ (134,648)	$ 3,427