Earnings per Share (Details) - $ / shares	3 Months Ended												12 Months Ended
	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, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share, Basic and Diluted [Abstract]
Basic earnings per common share (in dollars per share)	$ 0.76	$ 0.74	$ 0.70	$ 0.67	$ 0.65	$ 0.59	$ 0.54	$ 0.51	$ 0.45	$ 0.47	$ 0.35	$ 0.40	$ 2.88	$ 2.29	$ 1.68
Diluted earnings per common share (in dollars per share)	$ 0.76	$ 0.74	$ 0.70	$ 0.67	$ 0.65	$ 0.59	$ 0.54	$ 0.51	$ 0.45	$ 0.47	$ 0.35	$ 0.40	$ 2.86	$ 2.28	$ 1.67
Basic weighted average shares outstanding (in shares)													32,603,000	34,668,000	37,809,000
Diluted weighted average shares outstanding (in shares)													32,863,000	34,901,000	38,040,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount													0	0	135,000
Weighted Average Number of Shares Outstanding, Diluted [Abstract]
Basic weighted average shares outstanding (in shares)													32,603,000	34,668,000	37,809,000
Incremental shares for common stock equivalents (in shares)													260,000	233,000	231,000
Diluted shares outstanding (in shares)													32,863,000	34,901,000	38,040,000