Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Tax credit carryforwards	$ 20,272	$ 0	$ 0
Allowance for loan and lease losses	5,806	6,828	2,780
Mark to market on loans held for sale	5,751	0	0
Stock-based compensation expense	1,872	3,877	0
Goodwill and intangibles	1,259	0	0
Accrued expenses	375	725	505
Other	1,062	1,395	734
Total deferred tax assets	36,397	12,825	4,019
Deferred tax liabilities:
Investment in joint venture	16,320	0	0
Unguaranteed loan discount	6,615	4,644	4,083
Premises and equipment	24,112	7,193	3,952
Deferred loan fees and costs, net	1,139	1,321	892
Other	323	0	0
Total deferred tax liabilities	48,509	13,158	8,927
Net deferred tax liability	$ 12,112	$ 333	$ 4,908