CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands		Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income
Balance at period start (in shares) at Dec. 31, 2017			45,776
Balance at period start at Dec. 31, 2017		$ 447,719	$ 458	$ 593,295	$ (148,178)	$ 2,144
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation (in shares)			272
Stock-based compensation		1,438	$ 1	1,437
Purchase of common stock for retirement (in shares)			(29)
Purchase of common stock for retirement		(543)		(543)
Other comprehensive income (loss)		0
Net income (loss)		15,185			15,185
Balance at period end (in shares) at Mar. 31, 2018			46,019
Balance at period end at Mar. 31, 2018		463,799	$ 459	594,189	(132,993)	2,144
Balance at period start (in shares) at Dec. 31, 2017			45,776
Balance at period start at Dec. 31, 2017		447,719	$ 458	593,295	(148,178)	2,144
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		25,541
Balance at period end (in shares) at Sep. 30, 2018			46,009
Balance at period end at Sep. 30, 2018		477,406	$ 460	597,439	(122,637)	2,144
Balance at period start (in shares) at Mar. 31, 2018			46,019
Balance at period start at Mar. 31, 2018		463,799	$ 459	594,189	(132,993)	2,144
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation (in shares)			(8)
Stock-based compensation		1,664	$ 1	1,663
Purchase of common stock for retirement (in shares)			(3)
Purchase of common stock for retirement		(21)		(21)
Other comprehensive income (loss)		0
Net income (loss)		16,178			16,178
Balance at period end (in shares) at Jun. 30, 2018			46,008
Balance at period end at Jun. 30, 2018		481,620	$ 460	595,831	(116,815)	2,144
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation (in shares)			15
Stock-based compensation		1,696		1,696
Purchase of common stock for retirement (in shares)			(14)
Purchase of common stock for retirement		(88)		(88)
Other comprehensive income (loss)		0
Net income (loss)		(5,822)			(5,822)
Balance at period end (in shares) at Sep. 30, 2018			46,009
Balance at period end at Sep. 30, 2018		477,406	$ 460	597,439	(122,637)	2,144
Balance at period start (in shares) at Dec. 31, 2018			46,984
Balance at period start at Dec. 31, 2018		512,329	$ 470	617,937	(108,751)	2,673
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock for business combination (in shares)			2,364
Issuance of common stock for business combination		36,980	$ 23	36,957
Stock-based compensation (in shares)			246
Stock-based compensation		1,535	$ 3	1,532
Purchase of common stock for retirement (in shares)			(44)
Purchase of common stock for retirement		(734)		(734)
Net income (loss)		61,092			61,092
Balance at period end (in shares) at Mar. 31, 2019			49,550
Balance at period end at Mar. 31, 2019		611,202	$ 496	655,692	(47,659)	2,673
Balance at period start (in shares) at Dec. 31, 2018			46,984
Balance at period start at Dec. 31, 2018		512,329	$ 470	617,937	(108,751)	2,673
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		5,370
Balance at period end (in shares) at Sep. 30, 2019			51,168
Balance at period end at Sep. 30, 2019		579,510	$ 512	679,706	(103,381)	2,673
Balance at period start (in shares) at Mar. 31, 2019			49,550
Balance at period start at Mar. 31, 2019		611,202	$ 496	655,692	(47,659)	2,673
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock for convertible notes repurchase (in shares)	[1]		1,449
Issuance of common stock for convertible notes repurchase, net	[1]	17,789	$ 14	17,775
Issuance of common stock for employee stock purchase plan (in shares)			37
Issuance of common stock for employee stock purchase plan		754		754
Stock-based compensation (in shares)			(31)
Stock-based compensation		1,550		1,550
Purchase of common stock for retirement (in shares)			(2)
Purchase of common stock for retirement		(20)		(20)
Exercise of stock options (in shares)			21
Exercise of stock options		119		119
Net income (loss)		28,169			28,169
Balance at period end (in shares) at Jun. 30, 2019			51,024
Balance at period end at Jun. 30, 2019		659,563	$ 510	675,870	(19,490)	2,673
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation (in shares)			(20)
Stock-based compensation		1,448		1,448
Purchase of common stock for retirement (in shares)			(6)
Purchase of common stock for retirement		(414)		(414)
Exercise of stock options (in shares)			170
Exercise of stock options		2,804	$ 2	2,802
Net income (loss)		(83,891)			(83,891)
Balance at period end (in shares) at Sep. 30, 2019			51,168
Balance at period end at Sep. 30, 2019		$ 579,510	$ 512	$ 679,706	$ (103,381)	$ 2,673

[1] The issuance of common stock for the repurchase of a portion of our 5.00% Convertible Senior Notes in the three months ended June 30, 2019 is presented net of a $12.3 million write-off associated with the equity component of the repurchased notes.