Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2015

Quarterly Financial Data [Abstract]

Schedule of Quarterly Financial Information [Table Text Block]

	Three Months Ended
	December 31, 2015		September 30, 2015		June 30, 2015		March 31, 2015
Total revenues	$	178,058	$	124,618	$	138,066	$	149,706
Net income	$	100,574	$	69,459	$	78,264	$	84,498
Net income per basic share	$	0.61	$	0.42	$	0.48	$	0.52
Net income per diluted share	$	0.61	$	0.42	$	0.47	$	0.50

	Three Months Ended
	December 31, 2014		September 30, 2014		June 30, 2014		March 31, 2014
Total revenues	$	117,075	$	164,594	$	162,752	$	136,804
Net income	$	55,071	$	102,235	$	92,055	$	72,883
Net income per basic share	$	0.34	$	0.64	$	0.57	$	0.48
Net income per diluted share	$	0.32	$	0.61	$	0.52	$	0.44