Consolidated Statements of Changes in Shareholders' Equity (unaudited) - USD ($) $ in Thousands	Total	Common stock	Retained Earnings	Accumulated other comprehensive income (loss)
Beginning Balance at Dec. 31, 2013	$ 1,726,406	$ 1,488,126	$ 255,030	$ (16,750)
Balance (in shares) at Dec. 31, 2013		101,260,000
Increase (decrease) in stockholders' equity
Net income for common stock	87,068		87,068
Other comprehensive income, net of taxes	4,067			4,067
Issuance of common stock, net	5,310	$ 5,310
Issuance of common stock, net (in shares)		300,000
Common stock dividends ($0.62 per share)	(62,916)		(62,916)
Ending Balance at Jun. 30, 2014	1,759,935	$ 1,493,436	279,182	(12,683)
Balance (in shares) at Jun. 30, 2014		101,560,000
Beginning Balance at Dec. 31, 2014	$ 1,790,573	$ 1,521,297	296,654	(27,378)
Balance (in shares) at Dec. 31, 2014	102,565,266	102,565,000
Increase (decrease) in stockholders' equity
Net income for common stock	$ 66,884		66,884
Other comprehensive income, net of taxes	931			931
Issuance of common stock, net	105,272	$ 105,272
Issuance of common stock, net (in shares)		4,882,000
Common stock dividends ($0.62 per share)	(65,140)		(65,140)
Ending Balance at Jun. 30, 2015	$ 1,898,520	$ 1,626,569	$ 298,398	$ (26,447)
Balance (in shares) at Jun. 30, 2015	107,446,530	107,447,000