Other Employee Benefits - Schedule of Shares Purchased in Open Market for Employees (Details) - USD ($)													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
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense													$ 5,211,000	$ 5,912,000	$ 5,369,000
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares	3,717	4,991	3,617	4,617	6,822	4,939	5,443	4,322	3,931	5,246	5,180	4,961	16,942	21,526	19,318
Common Stock Fair Value	$ 24.80	$ 19.81	$ 28.10	$ 20.63	$ 18.61	$ 23.45	$ 25.72	$ 29.98	$ 36.87	$ 26.99	$ 34.38	$ 35.08	$ 22.90	$ 23.80	$ 33.06
Purchase Price	$ 21.08	$ 16.84	$ 23.89	$ 17.54	$ 15.82	$ 19.93	$ 21.86	$ 25.49	$ 31.34	$ 22.94	$ 29.22	$ 29.82	$ 19.46	$ 20.23	$ 28.10
Compensation Expense	$ 13,827	$ 14,823	$ 15,228	$ 14,267	$ 19,033	$ 17,385	$ 21,010	$ 19,406	$ 21,738	$ 21,246	$ 26,729	$ 26,095	$ 58,145	$ 76,834	$ 95,808