SCHEDULE II - FINANCIAL INFORMATION OF REGISTRANT- PARENT COMPANY ONLY - Statement of Operations - Parent Company Only (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2019
Sep. 30, 2019
Jun. 30, 2019
Mar. 31, 2019
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Revenues                      
Net investment income $ 7,962 $ 7,882 $ 7,629 $ 7,383 $ 6,952 $ 6,277 $ 5,735 $ 4,574 $ 30,856 $ 23,538 $ 16,273
Net realized investment gains 264 81 (113) (187) 6 (8) 59 0 45 57 208
Total revenues                 378,771 275,025 182,743
Expenses                      
Interest expense 2,974 2,979 3,071 3,061 3,028 2,972 5,560 3,419 12,085 14,979 13,528
Loss from change in fair value of warrant liability 2,632 (1,139) 1,685 5,479 (3,538) 5,464 (109) (420) 8,657 1,397 4,105
Total expenses                 162,118 139,064 129,951
Income before income taxes 62,789 63,932 50,958 38,974 45,244 31,847 32,339 26,531 216,653 135,961 52,792
Income tax expense 12,594 14,169 11,858 6,075 9,724 7,036 7,098 4,176 44,696 28,034 30,742
Net income $ 50,195 $ 49,763 $ 39,100 $ 32,899 $ 35,520 $ 24,811 $ 25,241 $ 22,355 171,957 107,927 22,050
Other comprehensive (loss) income, net of tax:                      
Unrealized gains (losses) in accumulated other comprehensive loss, net of tax expense (benefit) of $82, ($34), and ($49) for each of the years in the three-year period ended December 31, 2019, respectively                 32,155 (12,357) 2,559
Reclassification adjustment for losses (gains) included in net loss, net of tax (benefit) expense of $0, ($1) and $0 for each of the years in the three-year period ended December 31, 2019, respectively                 (35) 102 (131)
Other comprehensive income (loss), net of tax                 32,120 (12,255) 2,428
Comprehensive income                 204,077 95,672 24,478
Parent                      
Revenues                      
Net investment income                 1,124 1,145 691
Net realized investment gains                 1 5 1
Total revenues                 1,125 1,150 692
Expenses                      
Other operating expenses                 11,714 21,095 16,374
Interest expense                 0 2,227 0
Loss from change in fair value of warrant liability                 8,657 1,397 4,105
Total expenses                 20,371 24,719 20,479
Equity in net income of subsidiaries                 226,480 134,127 67,146
Income before income taxes                 207,234 110,558 47,359
Income tax expense                 35,277 2,631 25,309
Net income                 171,957 107,927 22,050
Other comprehensive (loss) income, net of tax:                      
Unrealized gains (losses) in accumulated other comprehensive loss, net of tax expense (benefit) of $82, ($34), and ($49) for each of the years in the three-year period ended December 31, 2019, respectively                 308 (128) (90)
Reclassification adjustment for losses (gains) included in net loss, net of tax (benefit) expense of $0, ($1) and $0 for each of the years in the three-year period ended December 31, 2019, respectively                 0 2 (1)
Equity in other comprehensive income (loss) of subsidiaries                 31,812 (12,129) 2,519
Other comprehensive income (loss), net of tax                 32,120 (12,255) 2,428
Comprehensive income                 $ 204,077 $ 95,672 $ 24,478