Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings per Share
Adjustments to net income (in dollars)	$ 0	$ 0	$ 0
Antidilutive securities (in shares)	0	0	0
Numerator:
Net income	$ 183,682	$ 230,178	$ 213,780
Denominator:
Basic: weighted-average shares outstanding (in shares)	139,560,305	139,487,762	139,459,620
Add: weighted-average equity-based awards (in shares)	96,688	4,846
Diluted: weighted-average shares outstanding (in shares)	139,656,993	139,492,608	139,459,620
Basic earnings per share (in dollars per share)	$ 1.32	$ 1.65	$ 1.53
Diluted earnings per share (in dollars per share)	$ 1.32	$ 1.65	$ 1.53