Reinsurance - Coverage and retention (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019		Dec. 31, 2018
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Amortization period		10 years
Variable Interest Entity, Not Primary Beneficiary
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Coverage		$ 3,425,833		$ 1,881,467
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2017-1 Ltd. (Oct-17)
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Aggregate reinsurance agreement	[1]	368,114
Coverage		216,429	[1]	304,373
First layer retention	[1]	165,652
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2018-1 Ltd. (Apr-18)
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Aggregate reinsurance agreement	[2]	374,460
Coverage		328,482	[2]	374,460
First layer retention	[2]	168,510
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2018-2 Ltd. (Aug-18)
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Aggregate reinsurance agreement	[3]	653,278
Coverage	[3]	437,009
First layer retention	[3]	352,258
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2018-3 Ltd. (Oct-18)
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Aggregate reinsurance agreement	[4]	506,110
Coverage		426,806	[4]	$ 506,110
First layer retention	[4]	179,331
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2019-1 Ltd. (Mar-19)
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Aggregate reinsurance agreement	[5]	341,790
Coverage	[5]	257,358
First layer retention	[5]	208,046
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2019-2 Ltd. (Apr-19)
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Aggregate reinsurance agreement	[6]	621,022
Coverage	[6]	525,959
First layer retention	[6]	221,794
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2019-3 Ltd. (Jul-19)
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Aggregate reinsurance agreement	[7]	700,920
Coverage	[7]	656,523
First layer retention	[7]	232,093
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2019-4 Ltd. (Oct-19)
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Aggregate reinsurance agreement	[8]	577,267
Coverage	[8]	577,267
First layer retention	[8]	$ 162,357

[1] Issued in October 2017, covering in-force policies issued between January 1, 2017 and June 30, 2017.

[2] Issued in April 2018, covering in-force policies issued between July 1, 2017 and December 31, 2017.

[3] Issued in August 2018, covering in-force policies issued between April 1, 2013 and December 31, 2015.

[4] Issued in October 2018, covering in-force policies issued between January 1, 2018 and June 30, 2018.

[5] Issued in March 2019, covering in-force policies primarily issued between 2005 to 2008 under United Guaranty Residential Insurance Company (“UGRIC”); as well as policies issued through 2015 under both UGRIC and Arch Mortgage Insurance Company.

[6] Issued in April 2019, covering in-force policies issued between July 1, 2018 and December 31, 2018.

[7] Issued in July 2019, covering in-force policies issued in 2016.

[8] Issued in October 2019, covering in-force policies issued between January 1, 2019 and June 30, 2019.