CONSOLIDATED STATEMENT OF CHANGES IN SHAREHOLDERS' EQUITY (Unaudited) - 9 months ended Sep. 30, 2015 - 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, 2014	$ 41,606	$ 409,984	$ 525,985	$ 30,720	$ (20,391)	$ 987,904
Balance (in shares) at Dec. 31, 2014	40,747,721
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income			71,159			71,159
Other comprehensive income, net of tax				15,187		15,187
Cash dividends declared:
Common, $0.91 per share			(37,123)			(37,123)
Common stock issued under employee stock plan, including tax benefits of $1,541	$ 323	8,065				8,388
Common stock issued under employee stock plan, including tax benefits of $1,541 (in shares)	322,879
Stock-based compensation		3,164				3,164
Treasury stock purchased					(9,125)	$ (9,125)
Treasury stock purchased (in shares)	(265,230)					(265,230)
Treasury stock issued to benefit plan					5,472	$ 5,472
Treasury stock issued to benefit plan (in shares)	213,653
Balance at Sep. 30, 2015	$ 41,929	$ 421,213	$ 560,021	$ 45,907	$ (24,044)	$ 1,045,026
Balance (in shares) at Sep. 30, 2015	41,019,023