Consolidated Statement Of Equity - USD ($)	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Cumulative Dividends In Excess Of Net Income [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Parent [Member]	Noncontrolling Interest [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 1,322,117,000	$ 415,000	$ 1,289,919,000	$ 32,605,000	$ (822,000)	$ 1,322,117,000	$ 0
Balance, shares at Dec. 31, 2017		41,532,154
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common stockholders				76,272,000	2,726,000	78,998,000
Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest							0
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ 78,998,000
Stock Issued During Period, Shares, New Issues	628,403
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture	11,309
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments	$ (2,427,000)		(2,427,000)			(2,427,000)
Stock Issued During Period, Value, New Issues	44,920,000	$ 7,000	44,913,000			44,920,000	0
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation	(325,000)		325,000			325,000	0
Share-based compensation	1,794,000		1,794,000			1,794,000	0
Dividends declared, $1.54 per share	(83,703,000)			(83,703,000)		(83,703,000)	0
Balance, shares at Dec. 31, 2017		41,532,154
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common stockholders	117,251,000
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	120,351,000
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	120,351,000
Balance, shares at Sep. 30, 2018		42,230,851
Cumulative Effect of New Accounting Principle in Period of Adoption				(235,000)	235,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common stockholders	40,979,000			40,979,000	374,000	41,353,000
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	41,353,000
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ 41,353,000
Stock Issued During Period, Shares, New Issues	39,669
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture	19,316
Stock Issued During Period, Value, New Issues	$ 2,973,000		2,973,000			2,973,000
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation	(405,000)		405,000			405,000
Share-based compensation	337,000		337,000			337,000
Dividends declared, $1.54 per share	(42,232,000)			(42,232,000)		(42,232,000)
Balance, shares at Sep. 30, 2018		42,230,851
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	1,363,400,000	$ 422,000	1,336,779,000	23,686,000	2,513,000	1,363,400,000	0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 1,389,713,000	$ 427,000	1,369,919,000	18,068,000	1,299,000	1,389,713,000	0
Balance, shares at Dec. 31, 2018	42,700,411	42,700,411
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common stockholders	$ 118,417,000
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	112,309,000
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ 112,305,000
Balance, shares at Sep. 30, 2019	43,956,238	43,956,238
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 1,462,993,000	$ 440,000	$ 1,467,289,000	$ (554,000)	$ (4,809,000)	$ 1,462,366,000	$ 627,000