Selected Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2019	[1]	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
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 82,457		$ 79,813	$ 79,624	$ 78,590	$ 76,589	$ 73,627	$ 71,581	$ 68,029	$ 320,484	$ 289,826	$ 260,642
Interest expense	18,045		18,617	18,797	18,234	16,747	14,365	13,178	11,097	73,693	55,388	34,909
Provision for loan losses	2,105		4,913	2,205	5,649	2,716	462	9,345	2,472	14,873	14,995	13,883
Net Interest Income After Provision for Loan Losses	62,307		56,283	58,622	54,707	57,126	58,800	49,058	54,460	231,918	219,443	211,850
Security (losses) gains, net	(26)		0	0	0	0	0	0	0	(26)	0	3,000
Noninterest income	15,257		13,063	12,901	11,362	11,095	12,042	12,251	13,792	52,558	49,181	55,462
Noninterest expense	50,178		37,667	40,352	38,919	36,415	37,085	35,863	36,082	167,116	145,445	147,907
Income Before Taxes	27,360		31,679	31,171	27,150	31,806	33,757	25,446	32,170
Provision for income taxes	5,091		4,743	5,070	4,222	4,952	2,876	4,010	6,007	19,126	17,845	46,437
Net Income Allocated to Common Shareholders	$ 22,269		$ 26,936	$ 26,101	$ 22,928	$ 26,854	$ 30,881	$ 21,436	$ 26,163	$ 97,974	$ 105,030	$ 72,726
Per Share Data
Common earnings per share-diluted (in USD per share)	$ 0.62		$ 0.79	$ 0.76	$ 0.66	$ 0.77	$ 0.88	$ 0.61	$ 0.75	$ 2.82	$ 3.01	$ 2.09
Dividends declared per common share (in USD per share)	0.28		0.27	0.27	0.27	0.27	0.25	0.25	0.22	$ 1.09	$ 0.99	$ 0.82
Common book value (in USD per share)	$ 30.13		$ 28.69	$ 28.11	$ 27.47	$ 26.98	$ 26.27	$ 25.91	$ 25.58

[1] The DNB Merger is included in our consolidated financial statements beginning on December 1, 2019.