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	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
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	58,624			58,470		154
Other comprehensive income	9,992				10,034	(42)
Stock issued	11,419	10,932				487
Stock purchased	(10,235)	(10,105)				(130)
Advance payments	415		415
Dividends declared	(14,041)			(14,041)
Balance at Sep. 30, 2013	$ 656,390	$ 310,835	$ 415	$ 498,199	$ (156,780)	$ 3,721