401(k) Additional Information (Details) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Compensation And Retirement Disclosure [Abstract]
Company matching cash contributions			50.00%
Maximum annual contributions per employee, Amount			$ 5,000
Expense for matching contributions	$ 300,000	$ 200,000	$ 1,400,000	$ 1,000,000

Amount of cost for defined contribution plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

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Balance Type:	debit
Period Type:	duration