Other Operating Expenses and Other Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Other Operating Expenses And Other Expenses [Abstract]
Amortization of policy acquisition costs	$ 31,614	$ 22,710	$ 59,252	$ 45,791
Other underwriting expenses of the operating segments	15,327	11,789	30,121	24,635
Other operating expenses of the Corporate and Other segment	6,095	5,475	12,556	10,727
Total	53,036	39,974	101,929	81,153
Other expenses	$ 346,000	$ 91,000	$ 232,000	$ 79,000