Other Liabilities - Components of Other Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Other Liabilities Disclosure [Abstract]
Pension liability	$ 37,789	$ 28,472
Low income housing tax credit fund commitments	9,146	8,554
Deferred compensation	9,450	6,605
Accrued salaries and benefits expense	8,990	6,619
Joint beneficiary agreements	3,558	3,365
Loan escrow and servicing payable	2,821	1,958
Deferred revenue	1,978	1,228
Litigation contingency		1,450
Miscellaneous other liabilities	8,345	8,171
Total other liabilities	$ 82,077	$ 66,422