Summary of Significant Accounting Policies (Calculations of Basic and Diluted EPS) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Summary of Significant Accounting Policies [Abstract]
Net income	$ 8,712	$ 19,677	$ 11,777	$ 5,126	$ 27,722	$ 35,730	$ 28,545	$ 15,939	$ 45,292	$ 107,936	$ 87,296
Weighted-average common shares outstanding - basic									48,981	48,562	47,851
Effect of diluted stock options and unvested restricted stock									685	552	738
Weighted-average common shares outstanding - diluted									49,666	49,114	48,589
Net income (loss) per share: Basic	$ 0.18	$ 0.40	$ 0.24	$ 0.11	$ 0.57	$ 0.74	$ 0.59	$ 0.33	$ 0.92	$ 2.22	$ 1.82
Net income (loss) per share: Diluted	$ 0.18	$ 0.40	$ 0.24	$ 0.10	$ 0.56	$ 0.73	$ 0.58	$ 0.33	$ 0.91	$ 2.20	$ 1.80
Anti-dilutive securities not included above									1,372	9	860