Consolidated Statement of Shareholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance at Dec. 31, 2011	$ 712,158	$ 348,383	$ 371,575	$ (7,800)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	57,288	0	58,779	(1,491)
Dividends paid on common stock	(48,007)	0	(48,007)	0
Tax expense from employee stock option plan	(149)	(149)	0	0
Stock-based compensation	1,291	1,291	0	0
Issuance of Common Stock	7,046	7,046	0	0
Balance at Dec. 31, 2012	729,627	356,571	382,347	(9,291)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	63,471	0	60,538	2,933
Dividends paid on common stock	(49,204)	0	(49,204)	0
Tax expense from employee stock option plan	(242)	(242)	0	0
Stock-based compensation	2,169	2,169	0	0
Issuance of Common Stock	6,051	6,051	0	0
Balance at Dec. 31, 2013	751,872	364,549	393,681	(6,358)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	54,974	0	58,692	(3,718)
Dividends paid on common stock	(50,093)	0	(50,093)	0
Tax expense from employee stock option plan	(117)	(117)	0	0
Stock-based compensation	1,646	1,646	0	0
Issuance of Common Stock	9,039	9,039	0	0
Balance at Dec. 31, 2014	$ 767,321	$ 375,117	$ 402,280	$ (10,076)