Earnings Per Common Share (Net Income, Weighted Average Common Shares Used in Calculating Basic Earnings Per Common Share and Diluted EPS) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Numerator
Net income	$ 220,318	$ 50,044
Deduct dividends paid	(32,448)	(18,834)
Undistributed earnings	$ 187,870	$ 31,210
Denominator
Weighted average shares outstanding used in basic earnings per share (in shares)	65,086,935	69,770,224
Incremental common shares from:
Weighted average shares used in diluted earnings per share calculations (in shares)	65,920,546	70,757,549
Earnings per common share - Basic
Distributed earnings, basic (in dollars per share)	$ 0.50	$ 0.27
Undistributed earnings, basic (in dollars per share)	2.88	0.45
Net income - basic (in dollars per share)	3.38	0.72
Earnings per common share - Diluted
Distributed earnings, diluted (in dollars per share)	0.49	0.27
Undistributed earnings, diluted (in dollars per share)	2.85	0.44
Net income - diluted (in dollars per share)	$ 3.34	$ 0.71
PSUs
Incremental common shares from:
Incremental common shares (in shares)	833,611	987,325