Consolidated Statements of Shareholders' Equity (USD $) In Thousands	Total	Common Stock	Restricted Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2011	$ 493,189	$ 1	$ 13,692	$ 67,422	$ 484,508	$ (72,434)
Beginning Balance (in shares) at Dec. 31, 2011		83,142	487
Net income	185,543				185,543
Other comprehensive loss, net of tax	(13,699)					(13,699)
Excess tax benefits on stock-based compensation plans	645		645
Restricted stock activity	3,725		3,725
Restricted stock activity (in shares)		178	35
Dividends	(103,733)				(103,733)
Ending Balance at Dec. 31, 2012	565,670	1	18,062	67,422	566,318	(86,133)
Ending Balance (in shares) at Dec. 31, 2012		83,320	522
Net income	219,658				219,658
Other comprehensive loss, net of tax	(68,170)					(68,170)
Excess tax benefits on stock-based compensation plans	656		656
Restricted stock activity	4,732		4,732
Restricted stock activity (in shares)		194	(21)
Ending Balance at Dec. 31, 2013	722,546	1	23,450	67,422	785,976	(154,303)
Ending Balance (in shares) at Dec. 31, 2013		83,514	501
Net income	249,740				249,740
Other comprehensive loss, net of tax	(31,941)					(31,941)
Excess tax benefits on stock-based compensation plans	1,028		1,028
Restricted stock activity	6,457		6,457
Restricted stock activity (in shares)		228	63
Ending Balance at Dec. 31, 2014	$ 947,830	$ 1	$ 30,935	$ 67,422	$ 1,035,716	$ (186,244)
Ending Balance (in shares) at Dec. 31, 2014		83,742	564