Defined Contribution Plan (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Contribution Plan
Employer's matching contribution to the plan	$ 5.2	$ 6.0	$ 6.8
Percentage of participant's eligible compensation for discretionary nonelective contribution	2.00%	2.00%
Defined Contribution Plan Employer Discretionary Contribution Amount	$ 2.5	$ 2.6

Amount of cost for defined contribution plan.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-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

Name:	us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration