Segment Reporting - Schedule of Segment Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Net interest income	$ 52,755	$ 43,610	$ 152,701	$ 104,288
Provision for loan losses	1,818	(784)	3,198	(1,906)
Mortgage banking income	29,350	32,227	87,856	89,887
Net, change in fair value of mortgage servicing rights	(2,701)	(893)	(6,192)	(3,234)
Other noninterest income	7,706	6,486	21,729	17,911
Depreciation and amortization	1,013	1,097	3,251	3,090
Amortization of intangibles	777	558	2,432	1,073
Loss on sale of mortgage servicing rights				249
Other noninterest mortgage banking expense	25,087	25,848	74,055	73,007
Other noninterest expense	30,336	41,721	89,984	87,358
Income before income taxes	28,079	12,990	83,174	45,981
Income tax expense	6,702	4,602	19,978	16,601
Net income	21,377	8,388	63,196	29,380
Total assets	5,058,167	4,581,943	5,058,167	4,581,943	$ 4,727,713
Goodwill	137,190	138,910	137,190	138,910	$ 137,190
Banking Segment
Segment Reporting Information [Line Items]
Net interest income	52,733	43,741	153,173	103,596
Provision for loan losses	1,818	(784)	3,198	(1,906)
Mortgage banking income	7,417	7,498	20,419	20,282
Other noninterest income	7,706	6,486	21,729	17,911
Depreciation and amortization	896	972	2,864	2,697
Amortization of intangibles	777	558	2,432	1,073
Other noninterest mortgage banking expense	6,383	6,216	17,129	16,420
Other noninterest expense	30,336	41,721	89,984	87,358
Income before income taxes	27,646	9,042	79,714	36,147
Total assets	4,637,097	4,056,901	4,637,097	4,056,901
Goodwill	137,090	138,810	137,090	138,810
Mortgage Segment
Segment Reporting Information [Line Items]
Net interest income	22	(131)	(472)	692
Mortgage banking income	21,933	24,729	67,437	69,605
Net, change in fair value of mortgage servicing rights	(2,701)	(893)	(6,192)	(3,234)
Depreciation and amortization	117	125	387	393
Loss on sale of mortgage servicing rights				249
Other noninterest mortgage banking expense	18,704	19,632	56,926	56,587
Income before income taxes	433	3,948	3,460	9,834
Total assets	421,070	525,042	421,070	525,042
Goodwill	$ 100	$ 100	$ 100	$ 100