Earnings Per Common Share Offerings (Details)			12 Months Ended
	Dec. 12, 2016 USD ($) $ / shares shares	Sep. 19, 2012 USD ($) Tangible_Equty_Unit	Dec. 31, 2016 shares	Dec. 31, 2015 shares	Dec. 31, 2014 shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Weighted average shares—Basic			57,324,000	56,734,000	55,305,000
Tangible Equity Units [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
TEUs Issued During Period, TEUs, New Issues | Tangible_Equty_Unit		2,300,000
TEUs, Stated Amount, Per Unit Value | $		$ 100
Tangible Equity Units [Member] | Underwriter's exercise of over-allotment option [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
TEUs Issued During Period, TEUs, New Issues | Tangible_Equty_Unit		300,000
Settlement of the prepaid stock purchase contract component of the TEUs [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Weighted average shares—Basic					2,841,650
Class A Common Stock [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Weighted average shares—Basic			131,148
Class A Common Stock [Member] | Common Stock [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Stock issued during period, shares	4,000,000		4,000,000
Shares Issued, Price Per Share | $ / shares	$ 75.00
Net proceeds from issuance of common stock | $	$ 285,800,000
Weighted average shares—Basic				3,539,240
Class A Common Stock [Member] | Settlement of the prepaid stock purchase contract component of the TEUs [Member] | Common Stock [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Conversion of shares to Class A Common Stock, shares				3,539,240