CONSOLIDATED STATEMENT OF CHANGES IN SHAREHOLDERS' EQUITY (Unaudited) - 6 months ended Jun. 30, 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			50,260			50,260
Other comprehensive income, net of tax				61,800		61,800
Cash dividends declared:
Common, $0.62 per share			(27,292)			(27,292)
Common stock issued under employee stock plan, including tax benefits of $928	$ 253	3,629				3,882
Common stock issued under employee stock plan, including tax benefits of $928 (in shares)	253,410
Stock-based compensation		2,220				2,220
Treasury stock issued to benefit plan, net		1,704			3,708	5,412
Treasury stock issued to benefit plan, net (in shares)	150,425
Balance at Jun. 30, 2016	$ 44,696	$ 535,568	$ 589,559	$ 81,035	$ (13,929)	$ 1,236,929
Balance (in shares) at Jun. 30, 2016	44,178,695