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	51,124			51,015		109
Other comprehensive income (loss)	9,206				9,067	139
Stock issued	11,755	11,755
Stock purchased	(6,972)	(6,613)				(359)
Advance payments	517		517
Dividends declared	(10,624)			(10,624)
Balance at Jun. 30, 2017	785,895	353,913	517	615,771	(187,533)	3,227
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	65,745			65,585		160
Other comprehensive income (loss)	5,252				5,393	(141)
Stock issued	12,032	12,032
Stock purchased	(9,383)	(9,142)				(241)
Advance payments	542		542
Dividends declared	(11,737)			(11,737)
Balance at Jun. 30, 2018	824,797	$ 390,577	$ 542	674,562	$ (244,761)	$ 3,877
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of ASC 606, net of tax	$ 798			$ 798