CONSOLIDATED STATEMENT OF CHANGES IN SHAREHOLDERS' EQUITY (Unaudited) - 3 months ended Mar. 31, 2016 - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Treasury Stock [Member]	Total
Balance at Dec. 31, 2015	$ 44,443	$ 528,015	$ 566,591	$ 19,235	$ (17,637)	$ 1,140,647
Balance (in shares) at Dec. 31, 2015	43,774,860
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income			24,403			24,403
Other comprehensive income, net of tax				42,052		42,052
Cash dividends declared:
Common, $0.31 per share			(13,610)			(13,610)
Common stock issued under employee stock plan, including tax benefits of $594	$ 155	777				932
Common stock issued under employee stock plan, including tax benefits of $594 (in shares)	155,773
Stock-based compensation		1,219				1,219
Treasury stock issued to benefit plan		1,346			3,676	5,022
Treasury stock issued to benefit plan (in shares)	139,146
Balance at Mar. 31, 2016	$ 44,598	$ 531,357	$ 577,384	$ 61,287	$ (13,961)	$ 1,200,665
Balance (in shares) at Mar. 31, 2016	44,069,779