Revenue Recognition - Summary of Company's Revenue Streams (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Interest income:
Loans	$ 119,271	$ 85,625	$ 64,915	$ 289,069	$ 170,905
Investment securities and other interest-earning assets	9,605	7,074	5,246	23,333	13,416
Total interest income	128,876	92,699	70,161	312,402	184,321
Noninterest income:
Loan servicing fees	400	292	276	1,037	641
Earnings on bank-owned life insurance	1,270	617	629	2,498	1,654
Net gain from sales of loans	2,029	3,843	3,439	8,830	9,137
Net gain from sales of investment securities	1,063	330	896	1,399	2,989
Other income	530	753	936	2,697	2,370
Total noninterest income	7,544	8,151	8,221	23,361	21,663
Service charges on deposit accounts
Noninterest income:
Noninterest income	874	1,057	946	3,081	2,153
Other service fee income
Noninterest income:
Noninterest income	317	169	851	632	1,725
Debit card interchange fee income
Noninterest income:
Noninterest income	1,061	1,090	248	3,187	994
Within Scope
Noninterest income:
Other income	(446)	293	163	84	301
Total noninterest income	1,806	2,609	2,208	6,984	5,173
Total revenues	1,806	2,609	2,208	6,984	5,173
Within Scope | Service charges on deposit accounts
Noninterest income:
Noninterest income	874	1,057	946	3,081	2,153
Within Scope | Other service fee income
Noninterest income:
Noninterest income	317	169	851	632	1,725
Within Scope | Debit card interchange fee income
Noninterest income:
Noninterest income	1,061	1,090	248	3,187	994
Out of Scope
Interest income:
Loans	119,271	85,625	64,915	289,069	170,905
Investment securities and other interest-earning assets	9,605	7,074	5,246	23,333	13,416
Total interest income	128,876	92,699	70,161	312,402	184,321
Noninterest income:
Loan servicing fees	400	292	276	1,037	641
Earnings on bank-owned life insurance	1,270	617	629	2,498	1,654
Net gain from sales of loans	2,029	3,843	3,439	8,830	9,137
Net gain from sales of investment securities	1,063	330	896	1,399	2,989
Other income	976	460	773	2,613	2,069
Total noninterest income	5,738	5,542	6,013	16,377	16,490
Total revenues	$ 134,614	$ 98,241	$ 76,174	$ 328,779	$ 200,811