Investment Securities Available For Sale, at Fair Value - Weighted Average Life (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
0 to 5 years	$ 332,934	$ 1,359,894
Over 5 to 10 years	320,361	521,517
10+ years	71,431	124,729
Total	$ 724,726	$ 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