Consolidated Statements Of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock and Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]
Balance (in shares) at Dec. 31, 2013		13,099,356
Balance at Dec. 31, 2013	$ 572,448	$ 0	$ (60,086)	$ 632,534
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	233,255			233,255
Other comprehensive income (loss)	(79,074)		(79,074)
Cash dividends	(59,400)			(59,400)
Repurchases of common stock (in shares)		(664,254)
Repurchases of common stock	(248,509)	$ (2,312)		(246,197)
Stock-based compensation (in shares)		11,263
Stock-based compensation	2,321	$ 2,312		9
Balance (in shares) at Dec. 31, 2014		12,446,365
Balance at Dec. 31, 2014	421,041	$ 0	(139,160)	560,201
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	238,603			238,603
Other comprehensive income (loss)	(5,366)		(5,366)
Cash dividends	(70,763)			(70,763)
Repurchases of common stock (in shares)		(501,261)
Repurchases of common stock	(197,851)	$ (3,070)		(194,781)
Tax benefit from stock-based compensation	374	$ 374
Tax withholdings related to stock-based compensation (in shares)		(3,135)
Tax withholdings related to stock-based compensation	(1,199)	$ (3)		(1,196)
Stock-based compensation (in shares)		6,477
Stock-based compensation	$ 2,725	$ 2,699		26
Balance (in shares) at Dec. 31, 2015	11,948,446	11,948,446
Balance at Dec. 31, 2015	$ 387,564	$ 0	(144,526)	532,090
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	243,441			243,441
Other comprehensive income (loss)	(37,984)		(37,984)
Cash dividends	(75,829)			(75,829)
Repurchases of common stock (in shares)		(98,867)
Repurchases of common stock	(35,815)	$ (252)		(35,563)
Tax withholdings related to stock-based compensation (in shares)		(2,582)
Tax withholdings related to stock-based compensation	(1,076)	$ (1,076)		0
Stock-based compensation (in shares)		(1,025)
Stock-based compensation	$ 2,950	$ 2,931		19
Balance (in shares) at Dec. 31, 2016	11,845,972	11,845,972
Balance at Dec. 31, 2016	$ 483,251	$ 1,603	$ (182,510)	$ 664,158