CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Losses	Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period (in shares)		57,564,493
Balance at beginning of period (in shares)		58,037,554
Balance at beginning of period at Dec. 31, 2017	$ 506,063	$ 737	$ 653,435	$ 98,728	$ (2,385)	$ (244,452)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income for the year	21,272			21,272
Foreign currency translation and other	409				409
Stock-based compensation (in shares)		380,588
Stock-based compensation	2,657	$ 6	2,651
Stock repurchase	(5,412)					(5,412)
Equity component of convertible senior notes repurchase	(7,830)		(7,830)
Common stock dividends	(4,748)			(4,748)
Stock option exercises (in shares)		92,473
Stock option exercises	861	$ 1	860
Balance at end of period (in shares) at Mar. 31, 2018		58,037,554
Balance at end of period at Mar. 31, 2018	513,272	$ 744	649,116	115,252	(1,976)	(249,864)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period (in shares)		58,037,554
Balance at beginning of period (in shares)		55,135,788
Balance at beginning of period (in shares)		55,424,133
Balance at beginning of period at Dec. 31, 2018	473,849	$ 744	629,039	150,244	(3,343)	(302,835)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income for the year	14,780			14,780
Foreign currency translation and other	298				298
Stock-based compensation (in shares)		273,158
Stock-based compensation	2,586	$ 5	2,581
Stock repurchase	(2,635)					(2,635)
Common stock dividends	(4,512)			(4,512)
Unrealized loss on derivative instruments, net of tax	(814)				(814)
Stock option exercises (in shares)		15,187
Stock option exercises	54		54
Balance at end of period (in shares) at Mar. 31, 2019		55,424,133
Balance at end of period at Mar. 31, 2019	$ 483,606	$ 749	$ 631,674	$ 160,512	$ (3,859)	$ (305,470)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period (in shares)		55,424,133