Quarterly Results of Operations (Unaudited) - Summary of Quarterly Results of Operations (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	$ 143,857		$ 131,753		$ 123,963		$ 113,093		$ 108,370		$ 99,503		$ 99,375		$ 89,619		$ 512,666	$ 396,867	$ 335,250
Interest expense	40,711		33,653		28,579		21,982		20,459		18,340		16,991		14,861		124,925	70,651	55,811
Net interest income	103,146		98,100		95,384		91,111		87,911		81,163		82,384		74,758		387,741	326,216	279,439
Provision for credit losses	8,422		(1,365)		1,263		4,380		(4,475)		1,723		6,701		5,786		12,700	9,735	49,348
Noninterest income	21,007	[1]	23,976	[1]	24,672	[1]	24,983	[1]	25,656	[2]	27,124	[2]	22,989	[2]	24,105	[2]	94,638	99,874	88,403
Noninterest expense	72,696		61,231		62,435		61,939		66,371		56,530		56,134		54,321		258,301	233,356	220,180
Income before income taxes	43,035		62,210		56,358		49,775		51,671		50,034		42,538		38,756		211,378	182,999	98,314
Provision for income taxes	10,709		15,074		8,384		10,950		36,980		17,457		13,570		12,639		45,117	80,646	32,540
Net income	$ 32,326		$ 47,136		$ 47,974		$ 38,825		$ 14,691		$ 32,577		$ 28,968		$ 26,117		$ 166,261	$ 102,353	$ 65,774
Earnings per common share (Basic)	$ 0.39		$ 0.56		$ 0.57		$ 0.46		$ 0.18		$ 0.39		$ 0.35		$ 0.35		$ 1.99	$ 1.26	$ 0.88
Earnings per common share (Diluted)	$ 0.39		$ 0.56		$ 0.57		$ 0.46		$ 0.17		$ 0.39		$ 0.35		$ 0.35		$ 1.97	$ 1.25	$ 0.87

[1] Includes net securities gains (losses) of $(54) thousand, $2 thousand, $(1.8) million and $12 thousand during the fourth, third, second and first quarters of 2018, respectively.

[2] Includes net securities gains (losses) of $16 thousand, $1 thousand, $(244) thousand and $81 thousand during the fourth, third, second and first quarters of 2017, respectively