Investment Securities Available for Sale, at Fair Value - Weighted Average Lives for Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
0 to 5 years	$ 234,583	$ 332,934
Over 5 to 10 years	320,979	320,361
10+ years	40,733	71,431
Total	$ 596,295	$ 724,726

Debt Securities, Trading, Available-for-sale, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Fair Value

No definition available.

Name:	nymt_DebtSecuritiesTradingAvailableforsaleMaturityAllocatedandSingleMaturityDateafterFiveThroughTenYearsFairValue
Namespace Prefix:	nymt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant