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, 2016	$ 730,889	$ 348,771	$ 0	$ 575,380	$ (196,600)	$ 3,338
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	17,723			17,681		42
Other comprehensive income (loss)	3,758				3,692	66
Stock issued	8,282	8,282
Stock purchased	(3,984)	(3,629)				(355)
Advance payments	1,020		1,020
Dividends declared	(5,306)			(5,306)
Balance at Mar. 31, 2017	752,382	353,424	1,020	587,755	(192,908)	3,091
Balance at Dec. 31, 2017	761,548	387,687	0	619,916	(250,154)	4,099
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	21,164			21,093		71
Other comprehensive income (loss)	2,290				2,369	(79)
Stock issued	8,416	8,416
Stock purchased	(4,898)	(4,662)				(236)
Advance payments	1,070		1,070
Dividends declared	(5,874)			(5,874)
Balance at Mar. 31, 2018	784,514	$ 391,441	$ 1,070	635,933	$ (247,785)	$ 3,855
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of ASC 606, net of tax	$ 798			$ 798