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401(k) plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
Matching contribution (as a percent of total salary)	100.00%	92.00%	84.00%
Percentage of employee's base salary, matched by employer	6.00%
Expense recorded	$ 3.5	$ 2.2	$ 1.6

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- References

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- Definition

Amount of cost for defined contribution plan.

+ References

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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- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

+ References

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- Definition

Percentage employer matches of the employee's percentage contribution matched.

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