Quarterly Results of Operations (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 108,653	$ 104,800	$ 100,871	$ 93,620	$ 90,348	$ 84,847	$ 71,467	$ 68,234	$ 407,944	$ 314,896	$ 253,312
Interest expense	20,769	18,314	16,300	13,704	11,583	10,427	8,367	7,235	69,087	37,612	26,839
NET INTEREST INCOME	87,884	86,486	84,571	79,916	78,765	74,420	63,100	60,999	338,857	277,284	226,473
Provision for loan losses	1,664	1,400	1,663	2,500	1,800	2,083	2,875	2,385	7,227	9,143	5,657
NET INTEREST INCOME AFTER PROVISION FOR LOAN LOSSES	86,220	85,086	82,908	77,416	76,965	72,337	60,225	58,614	331,630	268,141	220,816
Non-interest income	19,180	19,527	18,191	19,561	19,061	18,668	18,434	14,846	76,459	71,009	65,203
Non-interest expense	57,738	55,022	53,504	53,687	56,433	58,708	47,316	43,099	219,951	205,556	177,359
INCOME BEFORE INCOME TAX	47,662	49,591	47,595	43,290	39,593	32,297	31,343	30,361
Income tax expense	5,949	8,478	7,961	6,611	15,210	7,939	7,207	7,168	28,999	37,524	27,609
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS	$ 41,713	$ 41,113	$ 39,634	$ 36,679	$ 24,383	$ 24,358	$ 24,136	$ 23,193	$ 159,139	$ 96,070	$ 81,051
Basic EPS (in dollars per share)	$ 0.85	$ 0.83	$ 0.80	$ 0.75	$ 0.49	$ 0.50	$ 0.57	$ 0.57	$ 3.23	$ 2.13	$ 1.99
Diluted EPS (in dollars per share)	$ 0.85	$ 0.83	$ 0.80	$ 0.74	$ 0.49	$ 0.50	$ 0.57	$ 0.56	$ 3.22	$ 2.12	$ 1.98
Average Shares Outstanding:
Basic (in shares)	49,314,276	49,286,945	49,252,580	49,192,647	49,144,310	48,431,880	42,038,824	40,984,481	49,262,015	45,181,221	40,767,343
Diluted (in shares)	49,511,233	49,492,019	49,451,406	49,427,972	49,379,303	48,643,774	42,243,539	41,220,586	49,470,923	45,402,978	41,013,133