Parent-Only Financial Information - Condensed Statements of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Interest expense – borrowings									$ 14,391	$ 13,574	$ 7,275
Operating expenses									189,142	186,337	126,520
Benefit for income taxes	$ (3,181)	$ (6,302)	$ (4,465)	$ (4,836)	$ (4,269)	$ (5,278)	$ (3,018)	$ (1,005)	(18,784)	(13,570)	(22,855)
Net income	$ 23,450	$ 24,971	$ 18,980	$ 21,173	$ 26,732	$ 24,071	$ 15,702	$ 5,427	88,574	71,932	42,470
OceanFirst Financial Corp.
Condensed Financial Statements, Captions [Line Items]
Dividend income – subsidiary Bank									79,000	32,000	32,000
Interest and dividend income – investment securities									63	63	63
Interest income – advances to subsidiary Bank									426	525	280
Interest income – ESOP loan receivable									321	321	321
Other income									0	15	0
Total income									79,810	32,924	32,664
Interest expense – borrowings									5,402	4,997	2,592
Operating expenses									2,686	2,397	1,788
Income before income taxes and undistributed earnings of subsidiary Bank									71,722	25,530	28,284
Benefit for income taxes									924	846	973
Income before undistributed earnings of subsidiary Bank									72,646	26,376	29,257
Undistributed earnings of subsidiary Bank									15,928	45,556	13,213
Net income									$ 88,574	$ 71,932	$ 42,470