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					22,947
Foreign currency translation adjustments					(453)
COMPREHENSIVE INCOME					22,494
BALANCE at Sep. 30, 2018	114	150,905	72,606	(4,298)	219,327
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]
Prior period accounting reclassification			552	(552)
Components of comprehensive income:
Net income			8,677		8,677
Foreign currency translation adjustments				62	62
COMPREHENSIVE INCOME			9,229	(490)	8,739
Exercise of stock options		56			56
Dividends paid			(2,051)		(2,051)
BALANCE at Sep. 30, 2018	114	150,905	72,606	(4,298)	219,327
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					27,419
Foreign currency translation adjustments					(1,213)
COMPREHENSIVE INCOME					26,206
BALANCE at Sep. 30, 2019	114	151,055	102,621	(6,023)	247,767
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
Components of comprehensive income:
Net income			8,076		8,076
Foreign currency translation adjustments				(560)	(560)
COMPREHENSIVE INCOME			8,076	(560)	7,516
Dividends paid			(2,053)		(2,053)
BALANCE at Sep. 30, 2019	$ 114	$ 151,055	$ 102,621	$ (6,023)	$ 247,767