Parent Only Financial Statements - Statements of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net income	$ 2,273	$ 9,580	$ 9,616	$ 6,113	$ 6,517	$ 9,675	$ 3,324	$ 3,787	$ 5,048	$ 2,762	$ 2,942	$ 2,626	$ 27,582	$ 23,303	$ 13,378
Other comprehensive income (loss):
Unrealized holding gains (losses) on securities arising during the period													1,717	(6,697)	(3,746)
Other comprehensive income (loss) before tax													1,717	(6,697)	(3,746)
Income tax (expense) benefit related to items of other comprehensive income													(707)	2,122	1,542
Other comprehensive income (loss)													1,010	(4,575)	(2,204)
Less: Reclassification adjustment for gains (loss) included in net earnings														(1,043)
Income tax (expense) benefit related to reclassification adjustment														409
Reclassification adjustment for gains included in net earnings, net of tax														634
Other comprehensive income (loss), net of tax													1,010	(3,941)	(2,204)
Total comprehensive income													28,592	19,362	(2,204)
FFI
Net income													27,582	23,303	13,378
Other comprehensive income (loss):
Unrealized holding gains (losses) on securities arising during the period													1,717	(6,697)	(3,746)
Other comprehensive income (loss) before tax													1,717	(6,697)	(3,746)
Income tax (expense) benefit related to items of other comprehensive income													(707)	2,122	1,542
Other comprehensive income (loss)													1,010	(4,575)	(2,204)
Less: Reclassification adjustment for gains (loss) included in net earnings														1,043	(61)
Income tax (expense) benefit related to reclassification adjustment														(409)	25
Reclassification adjustment for gains included in net earnings, net of tax														634	(36)
Other comprehensive income (loss), net of tax													1,010	(3,941)	(2,240)
Total comprehensive income													$ 28,592	$ 19,362	$ 11,138