CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Earnings (Deficit)
Balance at Dec. 31, 2017	$ 591,548	$ 436	$ 628,983	$ (6,363)	$ (31,508)
Balance (in shares) at Dec. 31, 2017		43,587,079
Net income	10,979				10,979
Issuance of common stock for debt conversion	0	$ 0	0
Issuance of common stock for debt conversion (in shares)		2
Exercise of stock options and releases of restricted stock	2,375	$ 3	2,372
Exercise of stock options and releases of restricted stock (in shares)		266,308
Stock-based compensation expense	7,672		7,672
Cumulative effect of accounting changes at Dec. 31, 2017	(677)				(677)
Translation adjustment at Dec. 31, 2017	(5,410)			(5,410)
Balance at Sep. 30, 2018	606,487	$ 439	639,027	(11,773)	(21,206)
Balance (in shares) at Sep. 30, 2018		43,853,389
Balance at Jun. 30, 2018	598,659	$ 438	635,364	(11,143)	(26,000)
Balance (in shares) at Jun. 30, 2018		43,798,572
Net income	4,794				4,794
Exercise of stock options and releases of restricted stock	885	$ 1	884
Exercise of stock options and releases of restricted stock (in shares)		54,817
Stock-based compensation expense	2,779		2,779
Translation adjustment at Jun. 30, 2018	(630)			(630)
Balance at Sep. 30, 2018	606,487	$ 439	639,027	(11,773)	(21,206)
Balance (in shares) at Sep. 30, 2018		43,853,389
Balance at Dec. 31, 2018	615,568	$ 439	642,590	(11,893)	(15,568)
Balance (in shares) at Dec. 31, 2018		43,917,378
Net income	17,807				17,807
Issuance of common stock for debt conversion	198,757	$ 23	198,734
Issuance of common stock for debt conversion (in shares)		2,316,229
Reduction for equity component from debt conversion, net of tax	(200,079)		(200,079)
Exercise of stock options and releases of restricted stock	1,058	$ 3	1,055
Exercise of stock options and releases of restricted stock (in shares)		311,299
Issuance of common stock pursuant to the acquisition of C Technologies, Inc.	53,938	$ 8	53,930
Issuance of common stock pursuant to the acquisition of C Technologies, Inc., (in shares)		779,221
Tax withholding on vesting of restricted stock units	(290)		(290)
Tax withholding on vesting of restricted stock units (in shares)		(3,077)
Equity component of 0.375% senior convertible notes, net of tax	38,088		38,088
Proceeds from issuance of common stock, net of issuance costs	320,713	$ 48	320,665
Proceeds from issuance of common stock, net of issuance costs (in shares)		4,731,531
Stock-based compensation expense	9,459		9,459
Translation adjustment at Dec. 31, 2018	(9,901)			(9,901)
Balance at Sep. 30, 2019	1,045,118	$ 521	1,064,152	(21,794)	2,239
Balance (in shares) at Sep. 30, 2019		52,052,581
Balance at Jun. 30, 2019	878,968	$ 481	892,960	(15,053)	580
Balance (in shares) at Jun. 30, 2019		48,086,422
Net income	1,659				1,659
Issuance of common stock for debt conversion	198,755	$ 23	198,732
Issuance of common stock for debt conversion (in shares)		2,316,200
Reduction for equity component from debt conversion, net of tax	(200,079)		(200,079)
Exercise of stock options and releases of restricted stock	494	$ 1	493
Exercise of stock options and releases of restricted stock (in shares)		66,036
Tax withholding on vesting of restricted stock units	(290)		(290)
Tax withholding on vesting of restricted stock units (in shares)		(3,077)
Equity component of 0.375% senior convertible notes, net of tax	38,088		38,088
Proceeds from issuance of common stock, net of issuance costs	131,089	$ 16	131,073
Proceeds from issuance of common stock, net of issuance costs (in shares)		1,587,000
Stock-based compensation expense	3,175		3,175
Translation adjustment at Jun. 30, 2019	(6,741)			(6,741)
Balance at Sep. 30, 2019	$ 1,045,118	$ 521	$ 1,064,152	$ (21,794)	$ 2,239
Balance (in shares) at Sep. 30, 2019		52,052,581