Equity - Narratives (Details) - USD ($)	1 Months Ended	3 Months Ended								12 Months Ended
	Sep. 30, 2014	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jun. 03, 2015	Oct. 01, 2013
Share-based Compensation Arrangement by Share-based Payment Award
Distributions declared per share (usd per share)		$ 0.99	$ 0.985	$ 0.98	$ 0.9742	$ 0.9646	$ 0.955	$ 0.954	$ 0.9525	$ 3.9292	$ 3.8261	$ 3.685
Distributions payable		$ 107,090,000				$ 102,715,000				$ 107,090,000	$ 102,715,000
Shares issued in public offering, shares	4,600,000
Proceeds from the issuance of common stock										$ 84,063,000	$ 0	$ 0
Common stock, per share value (usd per share)	$ 0.001	$ 0.001				$ 0.001				$ 0.001	$ 0.001
Share price	$ 64
Proceeds from issuance of shares in public offering	$ 282,200,000									$ 0	$ 0	282,162,000
Redeemable Noncontrolling Interest
Distributions to noncontrolling interests										$ (17,030,000)	(14,713,000)	$ (19,719,000)
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award
Shares issued in public offering, shares										1,249,836		4,600,000
Redeemable Noncontrolling Interest
Shares issued to a third party in connection with the redemption of a redeemable noncontrolling interest, shares					217,011					217,011
Redeemable Noncontrolling Interest
Redeemable Noncontrolling Interest
Distributions to noncontrolling interests										$ (13,418,000)	$ 0	$ (926,000)
Senior Unsecured Credit Facility
Share-based Compensation Arrangement by Share-based Payment Award
Repayments of debt	$ 225,800,000
Officers | WPCI
Redeemable Noncontrolling Interest
Minority interest ownership interest														7.70%
Underwriters options
Share-based Compensation Arrangement by Share-based Payment Award
Shares issued in public offering, shares	600,000
ATM
Share-based Compensation Arrangement by Share-based Payment Award
Common stock maximum offering, value		$ 314,400,000								$ 314,400,000			$ 400,000,000
Shares issued in public offering, shares										1,249,836
Weighted average share price (usd per dollar)										$ 68.52
Proceeds from the issuance of common stock										$ 84,400,000
Professional fees										$ 300,000