Investment Securities Available for Sale, at Fair Value - Weighted Average Lives for Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
0 to 5 years	$ 343,573	$ 1,359,894
Over 5 to 10 years	183,910	521,517
10+ years	76,214	124,729
Total	$ 603,697	$ 2,006,140

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