Summary of Significant Accounting Policies - Recent Accounting Guidance (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019	Dec. 31, 2015
Revenue:
Revenue									$ 442,575	$ 410,561	$ 266,980
Gross profit	$ 43,567	$ 39,913	$ 49,000	$ 47,156	$ 36,720	$ 39,751	$ 39,062	$ 34,714	179,636	150,247	99,598
Income from operations									59,959	47,842	16,623
Income before income taxes									54,705	43,831	11,024
Income tax provision									8,820	(83,128)	23
Net income	$ 8,463	$ 8,838	$ 14,669	$ 13,915	$ 91,680	$ 11,841	$ 13,932	$ 9,506	$ 45,885	$ 126,959	$ 11,001
Net income per share:
Basic (in dollars per share)	$ 0.26	$ 0.27	$ 0.46	$ 0.43	$ 2.88	$ 0.38	$ 0.46	$ 0.32	$ 1.42	$ 4.11	$ 0.38
Diluted (in dollars per share)	$ 0.25	$ 0.26	$ 0.43	$ 0.41	$ 2.68	$ 0.35	$ 0.42	$ 0.29	$ 1.35	$ 3.80	$ 0.36
Consolidated Balance Sheet
Deferred income taxes	$ 71,939				$ 83,148				$ 71,939	$ 83,148
Total assets	548,441				488,218				548,441	488,218
Deferred revenue	22,584				18,145				22,584	18,145
Total current liabilities	84,997				79,287				84,997	79,287
Total liabilities	140,104				134,608				140,104	134,608
Accumulated deficit	(157,260)				(204,745)				(157,260)	(204,745)
Total stockholders' equity	408,337				353,610				408,337	353,610	$ 201,455		$ 183,764
Total liabilities and stockholders' equity	548,441				$ 488,218				548,441	488,218
Cumulative adjustment increase in retained earnings	1,600								1,600
Product
Revenue:
Revenue									415,922
ASU 2018-11 | Total Adjustment
Consolidated Balance Sheet
Operating leases												$ 6,100
ASC 606 Adjustments
Revenue:
Revenue									(1,023)
Gross profit									(1,023)
Income from operations									(1,023)
Income before income taxes									(1,023)
Income tax provision									(165)
Net income									$ (858)
Net income per share:
Basic (in dollars per share)									$ (0.03)
Diluted (in dollars per share)									$ (0.03)
Consolidated Balance Sheet
Deferred income taxes	165								$ 165
Total assets	165								165
Deferred revenue	2,623								2,623
Total current liabilities	2,623								2,623
Total liabilities	2,623								2,623
Accumulated deficit	(2,458)								(2,458)
Total stockholders' equity	(2,458)								(2,458)
Total liabilities and stockholders' equity	165								165
ASC 606 Adjustments | Product
Revenue:
Revenue									(1,023)
ASC 606 Adjustments | ASU 2014-09
Consolidated Balance Sheet
Gross Reclassification Decrease In Contract With Customer Liability Due To New ASU Adoption	1,600								1,600
Cumulative adjustment increase in retained earnings	1,600								1,600
Pro Forma Under ASC 605
Revenue:
Revenue									441,552	$ 410,561	$ 266,980
Gross profit									178,613
Income from operations									58,936
Income before income taxes									53,682
Income tax provision									8,655
Net income									$ 45,027
Net income per share:
Basic (in dollars per share)									$ 1.39
Diluted (in dollars per share)									$ 1.32
Consolidated Balance Sheet
Deferred income taxes	72,104								$ 72,104
Total assets	548,606								548,606
Deferred revenue	25,207								25,207
Total current liabilities	87,620								87,620
Total liabilities	142,727								142,727
Accumulated deficit	(159,718)								(159,718)
Total stockholders' equity	405,879								405,879
Total liabilities and stockholders' equity	$ 548,606								548,606
Pro Forma Under ASC 605 | Product
Revenue:
Revenue									$ 414,899