Consolidated Statements of Cash Flow - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net income	$ 67,958	$ 56,740
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan and lease losses	5,950	4,500
Depreciation, amortization and accretion, net	13,220	14,363
Deferred income taxes	7,511	6,816
Stock-based compensation	1,748	1,622
Net gains on sale of real estate		(142)
Other gains	(13)	(12)
Originations of loans held for sale	(862)
Proceeds from sales of loans held for sale	465
Change in assets and liabilities:
Net (increase) decrease in other assets	(4,869)	14,761
Net decrease in other liabilities	(37,891)	(33,625)
Net cash provided by operating activities	53,217	65,023
Available-for-sale securities:
Proceeds from maturities and principal repayments	218,941	205,927
Purchases	(130,252)	(390,968)
Other investments:
Proceeds from sales	2,285	8,452
Purchases	(4,403)	(5,858)
Loans:
Net increase in loans and leases resulting from originations and principal repayments	(189,496)	(265,066)
Proceeds from sales of loans originated for investment	570	671
Proceeds from bank-owned life insurance		3,987
Purchases of premises, equipment and software	(3,446)	(1,032)
Proceeds from sales of premises and equipment		10
Purchases of mortgage servicing rights	(6,444)
Proceeds from sales of other real estate owned	332	635
Other	(594)	(550)
Net cash used in investing activities	(112,507)	(443,792)
Cash flows from financing activities
Net (decrease) increase in deposits	(249,700)	143,646
Net decrease in short-term borrowings		(9,151)
Dividends paid	(33,504)	(30,700)
Proceeds from employee stock purchase plan	342	528
Net cash (used in) provided by financing activities	(282,862)	104,323
Net decrease in cash and cash equivalents	(342,152)	(274,446)
Cash and cash equivalents at beginning of period	1,034,644	1,052,058
Cash and cash equivalents at end of period	692,492	777,612
Supplemental disclosures
Interest paid	15,100	7,457
Income taxes paid, net of income tax refunds	189	180
Noncash investing and financing activities:
Transfers from loans and leases to other real estate owned		524
Transfers from loans and leases to loans held for sale	$ 4	$ 659