Segments and Geographical Information - Long-lived assets by geographic region (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segments and Geographical Information
Total long-lived assets	$ 1,987	$ 2,293	$ 1,921
United States
Segments and Geographical Information
Total long-lived assets	817	930	1,295
South Korea
Segments and Geographical Information
Total long-lived assets	$ 1,170	$ 1,363	$ 626

Long-lived assets other than financial instruments, long-term customer relationships of a financial institution, mortgage and other servicing rights, deferred policy acquisition costs, and deferred tax assets.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 41
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-41

Name:	us-gaap_NoncurrentAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant