Allowance for Loan and Lease Losses - Changes in Allowance for Loan and Lease Losses (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, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in allowance for Loan and Lease Losses:
Total allowance at beginning of year				$ 35,755				$ 32,004	$ 35,755	$ 32,004	$ 28,997
Provisions charged to operations	$ 2,014	$ 402	$ 976	$ 769	$ 1,706	$ 782	$ 978	$ 855	4,161	4,321	2,945
Recoveries on loans and leases									2,429	2,139	2,843
Charge-offs on loans and leases									(2,574)	(2,709)	(2,781)
Total allowance at end of year	$ 39,771				$ 35,755				$ 39,771	$ 35,755	$ 32,004