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, 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
Balance at Dec. 31, 2015	688,146	326,482	0	548,780	(190,435)	3,319
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	70,987			70,809		178
Other comprehensive income (loss)	12,313				12,104	209
Stock issued	14,238	14,238
Stock purchased	(9,149)	(8,793)				(356)
Advance payments	954		954
Dividends declared	(14,962)			(14,962)
Balance at Sep. 30, 2016	$ 762,527	$ 331,927	$ 954	$ 604,627	$ (178,331)	$ 3,350