Supplemental Cash Flow Disclosures - Non-cash Investing and Financing Activities (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Supplemental Cash Flow Information [Abstract]
Real Estate Owned, Transfer to Real Estate Owned	$ 4,723,000	$ 4,334,000	$ 3,067,000
Cash paid during the year for:
Interest	56,005,000	40,071,000	21,552,000
Income taxes	21,787,000	23,826,000	27,902,000
Non-cash investing and financing activities:
Loans transferred to other real estate owned and repossessed assets	0	0	1,891,000
Fair value of loans transferred from held to maturity to available for sale	30,359,000	37,367,000	15,102,000
Transfer of Loans Held-for-sale to Portfolio Loans	482,000	0	0
Gross (decrease) increase in market value adjustment to securities available for sale	20,604,000	(5,319,000)	1,983,000
Gross increase (decrease) in market value adjustment to derivatives	935,000	336,000	(783,000)
Noncash or Part Noncash Acquisition, Value of Assets Acquired	(361,595,000)	(21,834,000)	(37,070,000)
Other Significant Noncash Transaction, Consideration Received	484,000	0	245,000
Treasury stock reissued	2,531,000	2,257,000	2,258,000
Investments Committed to Purchase, Not Yet Paid	25,484,000	0	0
Increase in Commitment to Limited Partnership	$ 1,469,000	$ 0	$ 0