CONSOLIDATED STATEMENT OF CHANGES IN SHAREHOLDERS' EQUITY (Unaudited) - 6 months ended Jun. 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			46,137			46,137
Other comprehensive income, net of tax				(12,050)		(12,050)
Cash dividends declared:
Common, $0.60 per share			(24,353)			(24,353)
Common stock issued under employee stock plan, including tax benefits of $1,063	$ 234	5,379				5,613
Common stock issued under employee stock plan, including tax benefits of $1,063 (in shares)	233,799
Stock-based compensation		2,150				2,150
Treasury stock purchased					(9,125)	$ (9,125)
Treasury stock purchased (in shares)	(265,230)					(265,230)
Treasury stock issued to benefit plan					4,063	$ 4,063
Treasury stock issued to benefit plan (in shares)	160,316
Balance at Jun. 30, 2015	$ 41,840	$ 417,513	$ 547,769	$ 18,670	$ (25,453)	$ 1,000,339
Balance (in shares) at Jun. 30, 2015	40,876,606