Condensed Consolidated Statements of Changes in Shareholders’ Equity - USD ($) $ in Thousands	Total	Common Stock	Common Stock Subscribed, Unissued	Retained Earnings	Accumulated Other Comprehensive Loss	Noncontrolling Interests
Balance at Dec. 31, 2013	$ 670,781	$ 317,767	$ 0	$ 489,740	$ (140,363)	$ 3,637
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	70,993			70,829		164
Other comprehensive income (loss)	4,735				4,887	$ (152)
Stock issued	12,067	12,067
Stock purchased	(13,500)	(13,212)				$ (288)
Advance payments	436		436
Dividends declared	(14,302)			(14,302)
Balance at Sep. 30, 2014	731,210	316,622	436	546,267	(135,476)	3,361
Balance at Dec. 31, 2014	681,981	317,199	0	513,672	(152,193)	3,303
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	66,036			65,859		177
Other comprehensive income (loss)	(1,874)				(1,436)	(438)
Stock issued	13,552	13,151				401
Stock purchased	(10,759)	(10,656)				(103)
Advance payments	470		470
Dividends declared	(14,418)			(14,418)
Balance at Sep. 30, 2015	$ 734,988	$ 319,694	$ 470	$ 565,113	$ (153,629)	$ 3,340