Equity (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Equity activity
Beginning balance			$ 660,121
Net income	$ 17,928	$ 18,273	35,480	$ 35,277
Vesting of stock option and restricted common stock			2,081	1,449
Stock option exercise			79
Reclassification adjustment	(8)	$ (9)	(17)	$ (18)
Preferred stock dividends			(1,636)
Common stock dividends			(36,247)
Other			(339)
Ending balance	$ 659,522		$ 659,522