Segment Reporting - Schedule of Segment Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Net interest income	$ 51,517	$ 30,427	$ 99,946	$ 60,678
Provision for loan losses	1,063	(865)	1,380	(1,122)
Mortgage banking income	30,322	32,079	58,506	57,660
Net, change in fair value of mortgage servicing rights	(1,778)	(1,840)	(3,491)	(2,341)
Other noninterest income	7,164	5,418	13,968	11,425
Depreciation and amortization	1,132	991	2,238	1,993
Amortization of intangibles	802	123	1,655	515
Loss on sale of mortgage servicing rights		249		249
Other noninterest mortgage banking expense	25,089	24,791	48,968	47,159
Other noninterest expense	29,280	22,982	59,593	45,637
Income before income taxes	29,859	17,813	55,095	32,991
Income tax expense	7,794	6,574	13,276	11,999
Net income	22,065	11,239	41,819	20,992
Total assets	4,923,249	3,346,570	4,923,249	3,346,570	$ 4,727,713
Goodwill	137,190	46,867	137,190	46,867	$ 137,190
Banking Segment
Segment Reporting Information [Line Items]
Net interest income	51,669	29,999	100,440	59,855
Provision for loan losses	1,063	(865)	1,380	(1,122)
Mortgage banking income	6,894	7,118	13,002	12,784
Other noninterest income	7,164	5,418	13,968	11,425
Depreciation and amortization	990	861	1,968	1,725
Amortization of intangibles	802	123	1,655	515
Other noninterest mortgage banking expense	5,649	5,368	10,746	10,204
Other noninterest expense	29,280	22,982	59,593	45,637
Income before income taxes	27,943	14,066	52,068	27,105
Total assets	4,443,469	2,878,437	4,443,469	2,878,437
Goodwill	137,090	46,767	137,090	46,767
Mortgage Segment
Segment Reporting Information [Line Items]
Net interest income	(152)	428	(494)	823
Mortgage banking income	23,428	24,961	45,504	44,876
Net, change in fair value of mortgage servicing rights	(1,778)	(1,840)	(3,491)	(2,341)
Depreciation and amortization	142	130	270	268
Loss on sale of mortgage servicing rights		249		249
Other noninterest mortgage banking expense	19,440	19,423	38,222	36,955
Income before income taxes	1,916	3,747	3,027	5,886
Total assets	479,780	468,133	479,780	468,133
Goodwill	$ 100	$ 100	$ 100	$ 100