Stockholders' Equity (Details) $ / shares in Units, $ in Thousands				1 Months Ended		4 Months Ended	12 Months Ended
	May 06, 2016 USD ($) sales_agent	Aug. 28, 2015 USD ($) sales_agent	Jun. 22, 2015 USD ($) $ / shares shares	Jul. 31, 2016 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) $ / shares shares	May 06, 2016 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) item $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($)
Changes In Equity And Comprehensive Income Line Items [Line Items]
Common stock, shares authorized (in shares)							500,000,000	500,000,000
Common stock, par value (in dollars per share) | $ / shares							$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)							50,000,000	50,000,000
Preferred stock, par value (in dollars per share) | $ / shares							$ 0.01	$ 0.01
Common stock, shares issued (in shares)							126,007,091	125,881,460
Common stock, shares outstanding (in shares)							126,007,091	125,881,460
Preferred stock, shares issued (in shares)							0	0
Preferred stock, shares outstanding (in shares)							0	0
Number of votes, common stockholder rights | item							1
Net proceeds from sale of stock | $			$ 416,611				$ 0	$ 123,424	$ 446,877
Public offering price (in dollars per share) | $ / shares			$ 68.15
Gross proceeds from issuance | $			$ 431,049
Underwriting discount and transaction costs | $			$ 14,438
“At the market” equity program
Changes In Equity And Comprehensive Income Line Items [Line Items]
Aggregate offering price | $	$ 400,000	$ 400,000
Number of sales agents | sales_agent	5	5
Common stock sold (in shares)				550,000	410,000	831,300	0
Average sales price (in dollars per share) | $ / shares				$ 92.04	$ 75.17	$ 89.66
Net proceeds from sale of stock | $				$ 50,062	$ 30,266	$ 73,360
Available for issuance | $							$ 349,375
Public offering
Changes In Equity And Comprehensive Income Line Items [Line Items]
Common stock sold (in shares)			6,325,000