RESERVES FOR LOSSES AND LOSS SETTLEMENT EXPENSES - Cumulative Paid Claims and Allocated Claim Adjustment Expenses (Details) - USD ($)
$ in Thousands

Dec. 31, 2025

Dec. 31, 2024

Dec. 31, 2023

Dec. 31, 2022

Dec. 31, 2021

Dec. 31, 2020

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2016

Liability for Claims and Claims Adjustment Expense [Line Items]

Liabilities for unpaid losses and loss settlement expenses, net of reinsurance

$ 1,612,566

Commercial other liability

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

1,133,333

All outstanding liabilities for unpaid losses and loss settlement expenses before 2016, net of reinsurance

15,406

Liabilities for unpaid losses and loss settlement expenses, net of reinsurance

811,208

Commercial fire and allied

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

1,384,872

All outstanding liabilities for unpaid losses and loss settlement expenses before 2016, net of reinsurance

890

Liabilities for unpaid losses and loss settlement expenses, net of reinsurance

130,890

Commercial automobile

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

1,647,507

All outstanding liabilities for unpaid losses and loss settlement expenses before 2016, net of reinsurance

628

Liabilities for unpaid losses and loss settlement expenses, net of reinsurance

256,254

Commercial workers' compensation

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

359,380

All outstanding liabilities for unpaid losses and loss settlement expenses before 2016, net of reinsurance

15,289

Liabilities for unpaid losses and loss settlement expenses, net of reinsurance

74,006

Personal

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

322,951

All outstanding liabilities for unpaid losses and loss settlement expenses before 2016, net of reinsurance

234

Liabilities for unpaid losses and loss settlement expenses, net of reinsurance

9,866

2016 | Commercial other liability

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

157,582

$ 141,445

$ 136,400

$ 126,561

$ 115,107

$ 102,757

$ 88,885

$ 63,526

$ 38,184

$ 13,782

2016 | Commercial fire and allied

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

142,044

142,038

141,008

142,248

141,104

139,353

137,907

132,429

125,962

92,895

2016 | Commercial automobile

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

173,673

173,661

172,928

171,380

168,950

164,341

148,224

128,156

103,528

66,013

2016 | Commercial workers' compensation

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

51,344

51,126

51,023

50,127

48,277

47,082

45,743

40,680

32,345

14,413

2016 | Personal

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

45,160

45,159

44,827

44,828

44,737

44,618

44,046

42,660

40,910

$ 32,999

2017 | Commercial other liability

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

159,008

148,295

138,127

128,430

111,085

91,984

70,500

43,172

17,716

2017 | Commercial fire and allied

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

160,543

160,487

159,456

159,286

157,512

152,219

145,900

137,058

99,484

2017 | Commercial automobile

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

229,444

228,129

228,749

223,076

212,947

197,893

166,170

126,644

81,311

2017 | Commercial workers' compensation

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

46,202

46,154

45,742

45,508

43,833

41,672

38,082

31,309

14,647

2017 | Personal

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

58,597

58,377

58,206

57,824

57,169

55,982

53,111

$ 42,135

2018 | Commercial other liability

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

191,737

179,469

158,851

130,942

105,515

79,168

44,772

16,200

2018 | Commercial fire and allied

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

146,015

145,954

145,021

141,841

137,794

133,703

123,559

92,770

2018 | Commercial automobile

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

250,815

249,009

244,284

235,519

211,123

187,405

138,092

81,572

2018 | Commercial workers' compensation

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

50,381

50,031

49,964

48,807

47,173

43,189

35,369

16,949

2018 | Personal

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

51,103

51,101

50,852

50,661

50,185

49,464

47,433

$ 37,410

2019 | Commercial other liability

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

159,813

138,236

127,650

102,510

72,179

46,986

18,221

2019 | Commercial fire and allied

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

154,217

153,893

151,739

150,196

142,342

136,084

100,980

2019 | Commercial automobile

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

270,603

268,355

264,151

246,801

205,614

153,244

91,919

2019 | Commercial workers' compensation

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

48,263

47,308

46,101

43,044

38,382

29,668

13,582

2019 | Personal

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

57,510

56,971

56,852

56,658

54,935

52,390

$ 40,544

2020 | Commercial other liability

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

130,020

110,931

98,592

60,114

43,596

17,011

2020 | Commercial fire and allied

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

207,336

205,357

197,602

192,902

173,055

128,704

2020 | Commercial automobile

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

181,079

174,175

161,798

138,158

109,686

67,660

2020 | Commercial workers' compensation

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

42,992

42,052

39,479

35,542

29,605

17,603

2020 | Personal

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

71,385

71,394

71,416

70,543

68,124

$ 54,181

2021 | Commercial other liability

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

111,221

90,607

59,278

33,642

12,434

2021 | Commercial fire and allied

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

169,172

161,705

154,242

140,406

97,451

2021 | Commercial automobile

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

160,062

146,436

128,283

99,116

64,381

2021 | Commercial workers' compensation

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

37,598

36,512

34,074

29,453

17,949

2021 | Personal

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

25,822

25,764

24,889

23,829

$ 20,298

2022 | Commercial other liability

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

112,472

69,896

42,168

10,468

2022 | Commercial fire and allied

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

158,616

150,710

138,479

96,160

2022 | Commercial automobile

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

139,429

124,853

95,785

62,477

2022 | Commercial workers' compensation

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

23,585

21,033

17,851

9,434

2022 | Personal

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

2,828

2,792

2,128

$ 551

2023 | Commercial other liability

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

70,767

41,847

9,335

2023 | Commercial fire and allied

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

119,537

106,083

75,304

2023 | Commercial automobile

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

110,254

85,483

56,175

2023 | Commercial workers' compensation

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

21,458

18,085

10,227

2023 | Personal

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

4,598

3,089

$ 297

2024 | Commercial other liability

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

30,442

10,732

2024 | Commercial fire and allied

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

74,052

58,228

2024 | Commercial automobile

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

81,488

51,283

2024 | Commercial workers' compensation

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

21,504

10,277

2024 | Personal

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

2,672

$ 617

2025 | Commercial other liability

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

10,271

2025 | Commercial fire and allied

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

53,340

2025 | Commercial automobile

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

50,660

2025 | Commercial workers' compensation

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

16,053

2025 | Personal

Liability for Claims and Claims Adjustment Expense [Line Items]

Cumulative paid losses and allocated loss settlement expenses, net of reinsurance

$ 3,276