Insurance Reserves - Changes in the liability for unpaid losses and LAE (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]    
Unpaid losses on known claims, balance at beginning of period $ 264,470 $ 238,412
IBNR losses, balance at beginning of period 312,516 306,641
LAE, balance at beginning of period 138,112 140,402
Total unpaid losses and LAE, balance at beginning of period 715,098 685,455
Reinsurance recoverables, balance at beginning of period (31,609) (17,130)
Unpaid losses and LAE, net of reinsurance recoverables, balance at beginning of period 683,489 668,325
Loss and LAE incurred, current accident year 273,408 277,044
Loss and LAE incurred, Prior accident years (8,856) (6,368)
Total loss and LAE incurred 264,552 270,676
Loss and LAE payments, current accident year (89,106) (96,869)
Loss and LAE payments, prior accident years (177,479) (179,319)
Total loss and LAE payments (266,585) (276,187)
Unpaid losses and LAE, net of reinsurance recoverables, balance at end of period 681,457 662,814
Add back reinsurance recoverables, balance at end of period 19,549 16,133
Total unpaid losses and LAE, balance at end of period 701,006 678,947
Unpaid losses on known claims, balance at end of period 247,940 233,303
IBNR losses, balance at end of period 318,281 307,932
LAE, balance at end of period $ 134,786 $ 137,712