Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings
Beginning Balance at Dec. 31, 2014	$ 290,260	$ 6	$ (49,996)	$ 207,429	$ (5,551)	$ 138,373
Balance (in shares) at Dec. 31, 2014		61,852,000	9,021,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(32,389)					(32,389)
Other Comprehensive Income (Loss), before Tax	(8,592)
Total other comprehensive loss	(8,251)				(8,251)
Comprehensive income (loss)	(40,640)
Issuance of common stock upon exercise of stock awards	$ 675	$ 0		675
Issuance of common stock upon exercise of stock awards (in shares)	405,000	793,000
Issuance of common stock and treasury shares as consideration for acquisition	$ 1,571		$ 2,686			(1,115)
Issuance of treasury shares as consideration for acquisition (in shares)			238,000
Acquisition of treasury shares	(4,897)		$ (4,897)
Acquisition of treasury shares (in shares)			764,000
Excess tax benefit derived from stock award exercises	(411)			(411)
Stock-based compensation expense	5,873			5,873
Ending Balance at Dec. 31, 2015	252,432	$ 6	$ (52,207)	213,566	(13,802)	104,869
Balance (in shares) at Dec. 31, 2015		62,645,000	9,547,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(3,136)
Comprehensive income (loss)	(3,411)
Ending Balance at Mar. 31, 2016	251,179
Beginning Balance at Dec. 31, 2015	252,432	$ 6	$ (52,207)	213,566	(13,802)	104,869
Balance (in shares) at Dec. 31, 2015		62,645,000	9,547,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(5,043)
Comprehensive income (loss)	(6,708)
Ending Balance at Jun. 30, 2016	249,048
Beginning Balance at Dec. 31, 2015	252,432	$ 6	$ (52,207)	213,566	(13,802)	104,869
Balance (in shares) at Dec. 31, 2015		62,645,000	9,547,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(817)
Comprehensive income (loss)	(2,683)
Ending Balance at Sep. 30, 2016	255,617
Beginning Balance at Dec. 31, 2015	252,432	$ 6	$ (52,207)	213,566	(13,802)	104,869
Balance (in shares) at Dec. 31, 2015		62,645,000	9,547,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	3,949					3,949
Other Comprehensive Income (Loss), before Tax	(7,168)
Total other comprehensive loss	(7,147)				(7,147)
Comprehensive income (loss)	(3,198)
Issuance of common stock upon exercise of stock awards	$ 1,770	$ 0		1,770
Issuance of common stock upon exercise of stock awards (in shares)	420,000	746,000
Issuance of common stock and treasury shares as consideration for acquisition	$ 2,012		$ 2,749			(737)
Issuance of treasury shares as consideration for acquisition (in shares)			244,000
Excess tax benefit derived from stock award exercises	3,572			3,572
Stock-based compensation expense	5,572			5,572
Ending Balance at Dec. 31, 2016	262,161	$ 6	$ (49,458)	224,480	(20,949)	108,082
Balance (in shares) at Dec. 31, 2016		63,391,000	9,303,000
Beginning Balance at Mar. 31, 2016	251,179
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(1,905)
Comprehensive income (loss)	(3,295)
Ending Balance at Jun. 30, 2016	249,048
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	4,225
Comprehensive income (loss)	4,024
Ending Balance at Sep. 30, 2016	255,617
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	4,765
Ending Balance at Dec. 31, 2016	262,161	$ 6	$ (49,458)	224,480	(20,949)	108,082
Balance (in shares) at Dec. 31, 2016		63,391,000	9,303,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	5,678
Comprehensive income (loss)	7,657
Ending Balance at Mar. 31, 2017	267,340
Beginning Balance at Dec. 31, 2016	262,161	$ 6	$ (49,458)	224,480	(20,949)	108,082
Balance (in shares) at Dec. 31, 2016		63,391,000	9,303,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	10,052
Comprehensive income (loss)	15,911
Ending Balance at Jun. 30, 2017	273,226
Beginning Balance at Dec. 31, 2016	262,161	$ 6	$ (49,458)	224,480	(20,949)	108,082
Balance (in shares) at Dec. 31, 2016		63,391,000	9,303,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	17,168
Comprehensive income (loss)	25,196
Ending Balance at Sep. 30, 2017	289,494
Beginning Balance at Dec. 31, 2016	262,161	$ 6	$ (49,458)	224,480	(20,949)	108,082
Balance (in shares) at Dec. 31, 2016		63,391,000	9,303,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	16,430					16,430
Other Comprehensive Income (Loss), before Tax	1,732
Total other comprehensive loss	1,720				1,720
Comprehensive income (loss)	18,150
Issuance of common stock upon exercise of stock awards	$ 1,421	$ 0		1,421
Issuance of common stock upon exercise of stock awards (in shares)	428,000	648,000
Issuance of common stock and treasury shares as consideration for acquisition	$ 4,678	$ 0	$ 4,561	385		(269)
Issuance of treasury shares as consideration for acquisition (in shares)		(36,000)	405,000
Acquisition of treasury shares	$ (10,976)		$ (10,976)
Acquisition of treasury shares (in shares)	1,121,928		1,122,000
Stock-based compensation expense	$ 6,820			6,820
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	2,291			2,093		198
Ending Balance at Dec. 31, 2017	284,545	$ 6	$ (55,873)	235,199	(19,229)	124,442
Balance (in shares) at Dec. 31, 2017		64,075,000	10,020,000
Beginning Balance at Mar. 31, 2017	267,340
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	4,374
Comprehensive income (loss)	8,253
Ending Balance at Jun. 30, 2017	273,226
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	7,116
Comprehensive income (loss)	9,284
Ending Balance at Sep. 30, 2017	289,494
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(738)
Ending Balance at Dec. 31, 2017	$ 284,545	$ 6	$ (55,873)	$ 235,199	$ (19,229)	$ 124,442
Balance (in shares) at Dec. 31, 2017		64,075,000	10,020,000