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, 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	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
Balance at Dec. 31, 2016	730,889	348,771	0	575,380	(196,600)	3,338
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	80,678			80,449		229
Other comprehensive income	15,958				15,730	228
Stock issued	15,219	14,592				627
Stock purchased	(11,816)	(11,424)				(392)
Advance payments	966		966
Dividends declared	(15,910)			(15,910)
Balance at Sep. 30, 2017	$ 815,984	$ 351,939	$ 966	$ 639,919	$ (180,870)	$ 4,030