SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ 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
Interest income	$ 113,703	$ 119,624	$ 122,144	$ 91,543	$ 87,910	$ 82,875	$ 79,167	$ 73,749	$ 447,014	$ 323,701	$ 277,194
Interest expense	13,710	15,026	16,125	9,018	7,618	6,641	5,999	5,278	53,879	25,536	18,334
Net interest income	99,993	104,598	106,019	82,525	80,292	76,234	73,168	68,471	393,135	298,165	258,860
Provision (benefit)	4,000	0	1,000	1,000	1,200	1,075	2,000	500	6,000	4,775	2,950
Total noninterest income	33,297	31,816	28,648	21,533	23,491	23,264	21,887	19,863	115,294	88,505	82,994
Total noninterest expenses	67,445	67,533	93,032	56,311	64,391	55,439	52,688	53,451	284,321	225,969	204,359
Provision for income taxes	14,368	17,036	10,007	11,522	8,258	9,969	9,249	6,828	52,933	34,304	47,341
Net Income	$ 47,477	$ 51,845	$ 30,628	$ 35,225	$ 29,934	$ 33,015	$ 31,118	$ 27,555	$ 165,175	$ 121,622	$ 87,204
Basic earnings per share (in dollars per share)	$ 1.38	$ 1.51	$ 0.89	$ 1.25	$ 1.08	$ 1.20	$ 1.13	$ 1.00	$ 5.03	$ 4.41	$ 3.19
Diluted earnings per share (in dollars per share)	$ 1.38	$ 1.51	$ 0.89	$ 1.25	$ 1.07	$ 1.20	$ 1.13	$ 1.00	$ 5.03	$ 4.40	$ 3.19
Weighted average common shares (basic) (in shares)	34,374,953	34,361,176	34,313,492	28,106,184	27,815,437	27,537,841	27,526,653	27,486,573	32,810,433	27,592,380	27,294,028
Common share equivalents (in shares)	46,245	39,390	41,878	54,466	58,576	63,499	54,525	67,381	45,801	61,428	78,076
Weighted average common shares (diluted) (in shares)	34,421,198	34,400,566	34,355,370	28,160,650	27,874,013	27,601,340	27,581,178	27,553,954	32,856,234	27,653,808	27,372,104
Gain (Loss) on Sales of Loans, Net		$ 951							$ 13,200	$ 3,600	$ 4,700
Total Unusual or infrequent Income Items	$ 0	951	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Acquisition Related Costs	0	705	24,696	1,032	8,046	2,688	434	0	$ 26,433	$ 11,168	$ 3,393
Adjustment for tax effect of previously incurred M&A expense				650
Total unusual or infrequent expense items	$ 0	$ 705	$ 24,696	$ 1,682	$ 8,046	$ 2,688	$ 434	$ 0