Supplemental Cash Flow Disclosures - Non-cash Investing and Financing Activities (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Supplemental Cash Flow Information [Abstract]
Unsettled Bank Owned Life Insurance Proceeds	$ 897	$ 320
Cash paid during the period for:
Interest	14,995	14,768
Income Taxes Paid, Net	17,394	15,750
Non-cash investing and financing activities:
Loans Transferred to Other Real Estate Owned and Repossessions	2,154	3,973
Fair value of loans transferred from held to maturity to held for sale	13,292	3,573
Gross increase in market value adjustment to securities available for sale	5,240	13,094
Gross (decrease) increase in market value adjustment to securities derivatives	(538)	981
Investments committed to purchase not settled	0	276
Stock Issued During Period, Value, Treasury Stock Reissued	2,258	0
Noncash or Part Noncash Acquisition, Value of Assets Acquired	$ 36,926	$ 0