Stockholder's Equity (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized (in shares)	400,000,000		400,000,000
Common stock, par value (in dollars per share)	$ 0.01		$ 0.01
Preferred stock, authorized (in shares)	100,000,000
Preferred stock, par value (in dollars per share)	$ 0.01
Net proceeds of common share issuance	$ 75,081,000	$ 2,075,000
Shares repurchase program, authorized repurchase amount, shares	3,000,000
Repurchased shares of stock pursuant to share repurchase authorization (in shares)	0
Long-Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock, net of issuance costs (in shares)	196,087
Weighted average offering price per share (in dollars per share)	$ 36.55
Restricted stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value per share (in dollars per share)	$ 40.29
Fair value of the restricted stock granted	$ 1,200,000
Vesting period for the restricted stock	5 years
Unrecognized compensation costs related to restricted stock issuances	$ 4,900,000
Compensation costs	$ 500,000	500,000
Remaining weighted average period	3 years 2 months
Restricted stock [Member] | Amended and Restated 2010 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized (in shares)	1,705,000
Remaining balance of shares available (in shares)	109,109
Minimum [Member] | Restricted stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value per share (in dollars per share)	$ 14.20
Maximum [Member] | Restricted stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value per share (in dollars per share)	$ 40.29
$250 Million ATM Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock aggregate offering price	$ 250,000,000
Common stock aggregate offering price, remaining	$ 47,600,000
Issuance of common stock, net of issuance costs (in shares)	1,988,801
$200 Million ATM Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock aggregate offering price		$ 200,000,000
Issuance of common stock, net of issuance costs (in shares)		59,234
$250 Million & $200 Million ATM Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued, price per share (in dollars per share)	$ 41.39	$ 35.02
Net proceeds of common share issuance	$ 81,100,000	$ 2,000,000
Total compensation to the applicable sales agents	$ 1,200,000	$ 30,000