Parent-Only Financial Information - Condensed Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Financial Statements, Captions [Line Items]
Net gain on equity investments	$ 24,487	$ (3,576)	$ 148	$ 155					$ 21,214	$ 267	$ (199)
Other income	11,032	11,755	11,282	13,542	$ 11,231	$ 11,543	$ 9,879	$ 9,512
Interest expense – borrowings									18,367	14,391	13,574
Operating expenses									246,431	189,142	186,337
(Provision) benefit for income taxes	(10,419)	2,608	(5,878)	(4,044)	(3,181)	(6,302)	(4,465)	(4,836)	(17,733)	(18,784)	(13,570)
Net income	$ 33,064	$ (4,926)	$ 18,638	$ 16,533	$ 23,450	$ 24,971	$ 18,980	$ 21,173	63,309	88,574	71,932
OceanFirst Financial Corp.
Condensed Financial Statements, Captions [Line Items]
Dividend income – subsidiary Bank									54,000	79,000	32,000
Interest and dividend income – investment securities									949	63	63
Interest income – advances to subsidiary Bank									403	426	525
Interest income – ESOP loan receivable									301	321	321
Net gain on equity investments									20,460	0	0
Other income									0	0	15
Total income									76,113	79,810	32,924
Interest expense – borrowings									10,592	5,402	4,997
Operating expenses									3,382	2,686	2,397
Income before income taxes and undistributed earnings of subsidiary Bank									62,139	71,722	25,530
(Provision) benefit for income taxes									(2,901)	924	846
Income before undistributed earnings of subsidiary Bank									59,238	72,646	26,376
Undistributed earnings of subsidiary Bank									4,071	15,928	45,556
Net income									$ 63,309	$ 88,574	$ 71,932