Consolidated Statements of Common Stockholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock	Capital in excess of Par	Retained earnings
Balance at Dec. 31, 2010	$ 657,624	$ 41,577	$ 610,579	$ 5,468
Increase (Decrease) in Stockholders' Equity
Net income	54,971			54,971
Stock/stock units issued through:
Stock purchase and reinvestment plans	8,126	401	7,725
Dividends declared	(26,732)			(26,732)
Balance at Dec. 31, 2011	693,989	41,978	618,304	33,707
Increase (Decrease) in Stockholders' Equity
Net income	55,681			55,681
Stock/stock units issued through:
Stock purchase and reinvestment plans	10,401	506	9,895
Dividends declared	(42,273)			(42,273)
Balance at Dec. 31, 2012	717,798	42,484	628,199	47,115
Increase (Decrease) in Stockholders' Equity
Net income	63,445			63,445
Stock/stock units issued through:
Stock purchase and reinvestment plans	11,886	560	11,326
Dividends declared	(43,006)			(43,006)
Balance at Dec. 31, 2013	$ 750,123	$ 43,044	$ 639,525	$ 67,554