CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Surplus	Accumulated Other Comprehensive Income (Loss)	Total
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment for adoption of new ASU | ASU 2014-09			$ (324)		$ (324)
BALANCE at Dec. 31, 2017	$ 114	$ 150,699	55,580	$ (3,293)	203,100
BALANCE at Dec. 31, 2017	114	150,699	55,256	(3,293)	202,776
Components of comprehensive income:
Net income			6,670		6,670
Foreign currency translation adjustments				817	817
COMPREHENSIVE INCOME			6,670	817	7,487
Issuance of common stock to non-employee directors		150			150
Dividends paid			(2,049)		(2,049)
BALANCE at Mar. 31, 2018	114	150,849	59,877	(2,476)	208,364
BALANCE at Dec. 31, 2017	114	150,699	55,580	(3,293)	203,100
BALANCE at Dec. 31, 2017	114	150,699	55,256	(3,293)	202,776
Components of comprehensive income:
Net income					14,270
Foreign currency translation adjustments					(515)
COMPREHENSIVE INCOME					13,755
BALANCE at Jun. 30, 2018	114	150,849	65,428	(3,808)	212,583
BALANCE at Mar. 31, 2018	114	150,849	59,877	(2,476)	208,364
Components of comprehensive income:
Net income			7,600		7,600
Foreign currency translation adjustments				(1,332)	(1,332)
COMPREHENSIVE INCOME			7,600	(1,332)	6,268
Dividends paid			(2,049)		(2,049)
BALANCE at Jun. 30, 2018	114	150,849	65,428	(3,808)	212,583
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment for adoption of new ASU | ASU 2016-02			4		4
BALANCE at Dec. 31, 2018	114	150,905	81,354	(4,810)	227,563
BALANCE at Dec. 31, 2018	114	150,905	81,358	(4,810)	227,567
Components of comprehensive income:
Net income			8,660		8,660
Foreign currency translation adjustments				277	277
COMPREHENSIVE INCOME			8,660	277	8,937
Issuance of common stock to non-employee directors		150			150
Dividends paid			(2,052)		(2,052)
BALANCE at Mar. 31, 2019	114	151,055	87,966	(4,533)	234,602
BALANCE at Dec. 31, 2018	114	150,905	81,354	(4,810)	227,563
BALANCE at Dec. 31, 2018	114	150,905	81,358	(4,810)	227,567
Components of comprehensive income:
Net income					19,343
Foreign currency translation adjustments					(653)
COMPREHENSIVE INCOME					18,690
BALANCE at Jun. 30, 2019	114	151,055	96,598	(5,463)	242,304
BALANCE at Mar. 31, 2019	114	151,055	87,966	(4,533)	234,602
Components of comprehensive income:
Net income			10,683		10,683
Foreign currency translation adjustments				(930)	(930)
COMPREHENSIVE INCOME			10,683	(930)	9,753
Dividends paid			(2,051)		(2,051)
BALANCE at Jun. 30, 2019	$ 114	$ 151,055	$ 96,598	$ (5,463)	$ 242,304