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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Movement in allowance for Loan and Lease Losses:
Total allowance at beginning of year				$ 39,771				$ 35,755	$ 39,771	$ 35,755	$ 32,004
Provisions charged to operations	$ 2,058	$ 272	$ 1,045	$ 567	$ 2,014	$ 402	$ 976	$ 769	3,942	4,161	4,321
Recoveries on loans and leases									2,137	2,429	2,139
Charge-offs on loans and leases									(2,440)	(2,574)	(2,709)
Total allowance at end of year	$ 43,410				$ 39,771				$ 43,410	$ 39,771	$ 35,755