Earnings Per Share - Calculation of EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Numerator:
Net income	$ 24,822	$ 51,916	$ 35,464	$ 55,953
Denominator:
Weighted-average number of common shares outstanding—basic	200,830,064	195,776,924	200,738,301	195,700,864
Weighted-average number of common shares outstanding—diluted	201,142,747	196,246,718	201,115,115	196,217,724
Earnings per share:
Basic earnings per share (in dollars per share)	$ 0.12	$ 0.27	$ 0.18	$ 0.29
Diluted earnings per share (in dollars per share)	$ 0.12	$ 0.26	$ 0.18	$ 0.29
Unvested restricted common stock [Member]
Denominator:
Unvested Stock/SARs/MSUs	80,538	134,737	143,882	181,803
Stock Appreciation Rights [Member]
Denominator:
Unvested Stock/SARs/MSUs	1,425	0	2,212	0
Shares related to unvested PSUs [Member]
Denominator:
Unvested Stock/SARs/MSUs	230,720	335,057	230,720	335,057
Stock Appreciation Rights (SARs) [Member]
Earnings Per Share [Line Items]
Antidilutive securities excluded from calculation (in shares)	262,461		262,461