Common Stock Incentive Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Plan disclosures
Share-based compensation costs recognized	$ 12,000,000	$ 10,400,000	$ 12,000,000
Additional disclosures
Remaining unamortized share-based compensation expense	$ 18,700,000
Vesting rights percentage	20.00%
Number of performance shares that vest based on the achievement of performance goals
Total award value relative to the MSCI US REIT Index (as a percent)	50.00%	50.00%	60.00%
TSR relative to NAREIT Freestanding Index (as a percent)	20.00%	20.00%	20.00%
Dividend per share growth rate (as a percent)	20.00%	20.00%
Debt-to-EBITDA ratio (as a percent)	10.00%	10.00%	20.00%
Stock options outstanding	0	0	0
Non-employee director | Less than six years of service
Additional disclosures
Years of service	6 years
Vesting rights percentage	33.33%
Non-employee director | Six years of service
Additional disclosures
Years of service	6 years
Vesting rights percentage	50.00%
Non-employee director | Seven years of service
Additional disclosures
Years of service	7 years
Vesting rights percentage	100.00%
Employee | Age 55 and below
Additional disclosures
Vesting rights percentage	20.00%
Employee | Age 56
Additional disclosures
Vesting rights percentage	25.00%
Eligible age of employees for vesting of awards	56 years
Employee | Age 57
Additional disclosures
Vesting rights percentage	33.33%
Eligible age of employees for vesting of awards	57 years
Employee | Age 58
Additional disclosures
Vesting rights percentage	50.00%
Eligible age of employees for vesting of awards	58 years
Employee | Age 59
Additional disclosures
Vesting rights percentage	100.00%
Eligible age of employees for vesting of awards	59 years
Employee | Age 60 and above
Additional disclosures
Eligible age of employees for vesting of awards	60 years
Maximum | Employee | Age 55 and below
Additional disclosures
Eligible age of employees for vesting of awards	55 years
Minimum | Non-employee director | Eight or more years of service
Additional disclosures
Years of service	8 years
Restricted Stock
Number of shares
Outstanding nonvested shares, beginning of year	456,282	527,176	722,263
Shares granted	260,171	161,949	262,655
Shares vested	(200,066)	(205,248)	(440,348)
Shares forfeited	(2,864)	(27,595)	(17,394)
Outstanding nonvested shares, end of each period	513,523	456,282	527,176
Weighted average price
Outstanding nonvested shares, beginning of year (in dollars per share)	$ 30.46	$ 29.02	$ 23.37
Shares granted (in dollars per share)	54.14	50.87	39.87
Shares vested (in dollars per share)	43.26	37.70	36.88
Shares forfeited (in dollars per share)	48.15	45.58	39.07
Outstanding nonvested shares, end of each period (in dollars per share)	$ 48.33	$ 30.46	$ 29.02
Restricted Stock | Employee
Number of shares
Shares granted	232,171
Additional disclosures
Granted shares that vest over five year service period	143,739
Granted shares that vest over four year service period	88,432
Performance Shares
Number of shares
Outstanding nonvested shares, beginning of year	115,121	59,405
Shares granted	58,575	55,716	71,705
Shares vested	(10,454)		(4,067)
Shares forfeited	(3,491)		(8,233)
Outstanding nonvested shares, end of each period	159,751	115,121	59,405
Weighted average price
Outstanding nonvested shares, beginning of year (in dollars per share)	$ 46.94	$ 41.46
Shares granted (in dollars per share)	55.07	52.78	$ 41.46
Shares vested (in dollars per share)	44.54		41.46
Shares forfeited (in dollars per share)	52.55		41.46
Outstanding nonvested shares, end of each period (in dollars per share)	$ 49.95	$ 46.94	$ 41.46
Additional disclosures
Remaining unamortized share-based compensation expense	$ 3,700,000
Awards vesting on the first and second January1 after the end of the three year performance period (as a percent)	50.00%
Restricted Stock Units
Number of shares
Outstanding nonvested shares, beginning of year	10,136
Shares granted	14,783	10,136
Shares vested	(6,459)
Outstanding nonvested shares, end of each period	18,460	10,136
Weighted average price
Outstanding nonvested shares, beginning of year (in dollars per share)	$ 52.21
Shares granted (in dollars per share)	52.76	$ 52.21
Shares vested (in dollars per share)	52.21
Outstanding nonvested shares, end of each period (in dollars per share)	$ 52.65	$ 52.21
Additional disclosures
Remaining unamortized share-based compensation expense	$ 752,000
2012 Plan
Plan disclosures
Plan term from the date of adoption	10 years
2012 Plan | Non-employee director
Number of shares
Shares granted	28,000
Additional disclosures
Granted shares that vest immediately	20,000
Granted shares that vest annually, in equal parts, over three year service period	8,000
2012 Plan | Maximum
Plan disclosures
Authorized shares	3,985,734