Supplemental Cash Flow Disclosures - Non-cash Investing and Financing Activities (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash paid during the year for:
Interest	$ 33,964,000	$ 56,005,000	$ 40,071,000
Income taxes	25,914,000	21,787,000	23,826,000
Non-cash investing and financing activities:
Real Estate Owned, Transfer to Real Estate Owned	3,865,000	4,723,000	4,334,000
Fair value of loans transferred from held to maturity to available for sale	37,305,000	30,359,000	37,367,000
Transfer of Loans Held-for-sale to Portfolio Loans	4,335,000	482,000	0
Gross (decrease) increase in market value adjustment to securities available for sale	19,911,000	20,604,000	(5,319,000)
Gross (decrease) increase in market value adjustment to derivatives	(4,467,000)	935,000	336,000
Investments Committed to Purchase, Not Yet Paid	(34,185,000)	25,484,000	0
Increase in Commitment to Limited Partnership	0	1,469,000	0
Noncash or Part Noncash Acquisition, Value of Assets Acquired	0	(361,595,000)	(21,834,000)
Other Significant Noncash Transaction, Consideration Received	(384,000)	484,000	0
Treasury stock reissued	$ 1,594,000	$ 2,531,000	$ 2,257,000