Consolidated Statements of Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common stock	Additional paid-in capital	Retained earnings
Beginning balance at Dec. 31, 2013
Increase (Decrease) in Stockholders' Equity
Issuance of common stock, shares		14,828,094
Issuance of common stock, including stock option exercises	$ 483,506	$ 148	$ 483,358
Cost of issuance of common stock	(15,071)		(15,071)
Dividends on common stock ($0.63 per share)	(27,398)			(27,398)
Share-based compensation	56		56
Net income	41,913			41,913
Common Stock, Dividends, Per Share, Cash Paid	$ 0.48
Ending balance at Mar. 31, 2014	1,268,433	571	1,226,927	40,935
Ending balance, shares at Mar. 31, 2014		57,114,763
Beginning balance at Dec. 31, 2014	1,326,911	572	1,227,091	99,248
Beginning balance, shares at Dec. 31, 2014	57,192,212	57,192,212
Increase (Decrease) in Stockholders' Equity
Issuance of common stock, shares		10,999
Issuance of common stock, including stock option exercises	27	0	27
Dividends on common stock ($0.63 per share)	(36,038)			(36,038)
Share-based compensation	57		57
Net income	12,424			12,424
Common Stock, Dividends, Per Share, Cash Paid	$ 0.08
Ending balance at Mar. 31, 2015	$ 1,303,381	$ 572	$ 1,227,175	$ 75,634
Ending balance, shares at Mar. 31, 2015	57,203,211	57,203,211