SCHEDULE II - Condensed Financial Information of Registrant (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets [Abstract]
Cash and cash equivalents	$ 206,912	$ 172,457
Other assets	80,227	94,379
Total assets	5,024,405	3,136,776	$ 2,756,695
Liabilities:
Accrued expenses	58,416	51,792
Senior debt	158,300	118,300
Junior subordinated debt	104,055	104,055
Other liabilities	46,464	41,879
Total liabilities	4,245,824	2,427,535
Commitments and contingent liabilities
Shareholders’ equity:
Class A common shares	6	6
Additional paid-in capital	657,875	645,310
Retained earnings	89,586	79,753
Accumulated other comprehensive income (loss)	31,114	(15,828)
Total shareholders’ equity	778,581	709,241	694,699	$ 693,221
Total liabilities and shareholders’ equity	5,024,405	3,136,776
Parent Company
Assets [Abstract]
Cash and cash equivalents	1,521	240	$ 2,849	$ 2,969
Investment in subsidiaries	987,221	882,407
Due from subsidiaries	7,371	5,775
Other assets	2,842	1,579
Total assets	998,955	890,001
Liabilities:
Accrued expenses	1,592	2,322
Senior debt	143,300	103,300
Junior subordinated debt	15,928	15,928
Notes payable to subsidiary	40,000	40,000
Due to subsidiaries	18,822	18,605
Other liabilities	732	605
Total liabilities	220,374	180,760
Commitments and contingent liabilities
Shareholders’ equity:
Class A common shares	6	6
Additional paid-in capital	657,875	645,310
Retained earnings	89,586	79,753
Accumulated other comprehensive income (loss)	31,114	(15,828)
Total shareholders’ equity	778,581	709,241
Total liabilities and shareholders’ equity	$ 998,955	$ 890,001