Segment Reporting - Schedule of Segment Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Net interest income	$ 48,429	$ 30,251
Provision for loan losses	317	(257)
Mortgage banking income	28,184	25,581
Net, change in fair value of mortgage servicing rights		(501)
Change in fair value of mortgage servicing rights	(1,713)
Other noninterest income	6,804	6,007
Depreciation and amortization	1,106	1,002
Amortization of intangibles	853	392
Other noninterest mortgage banking expense	23,879	22,368
Other noninterest expense	30,313	22,655
Income before income taxes	25,236	15,178
Income tax expense	5,482	5,425
Net income	19,754	9,753
Total assets	4,725,416	3,166,459	$ 4,727,713
Goodwill	137,190	46,867	$ 137,190
Banking Segment
Segment Reporting Information [Line Items]
Net interest income	48,771	29,856
Provision for loan losses	317	(257)
Mortgage banking income	6,108	5,666
Other noninterest income	6,804	6,007
Depreciation and amortization	978	864
Amortization of intangibles	853	392
Other noninterest mortgage banking expense	5,097	4,836
Other noninterest expense	30,313	22,655
Income before income taxes	24,125	13,039
Total assets	4,220,543	2,705,118
Goodwill	137,090	46,767
Mortgage Segment
Segment Reporting Information [Line Items]
Net interest income	(342)	395
Mortgage banking income	22,076	19,915
Net, change in fair value of mortgage servicing rights		(501)
Change in fair value of mortgage servicing rights	(1,713)
Depreciation and amortization	128	138
Other noninterest mortgage banking expense	18,782	17,532
Income before income taxes	1,111	2,139
Total assets	504,873	461,341
Goodwill	$ 100	$ 100