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, 2014	$ 1,790,573	$ 1,521,297	$ 296,654	$ (27,378)
Balance (in shares) at Dec. 31, 2014		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	(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		107,447,000
Beginning Balance at Dec. 31, 2015	$ 1,927,640	$ 1,629,136	324,766	(26,262)
Balance (in shares) at Dec. 31, 2015	107,460,406	107,460,000
Increase (decrease) in stockholders' equity
Net income for common stock	$ 76,480		76,480
Other comprehensive income, net of taxes	10,908			10,908
Issuance of common stock, net	18,002	$ 18,002
Issuance of common stock, net (in shares)		727,000
Common stock dividends	(66,848)		(66,848)
Ending Balance at Jun. 30, 2016	$ 1,966,182	$ 1,647,138	$ 334,398	$ (15,354)
Balance (in shares) at Jun. 30, 2016	108,187,063	108,187,000