Stockholders' Equity - Summary of Repurchases During the Period (Details) - USD ($)				1 Months Ended																																				12 Months Ended
	Jan. 01, 2017	Jan. 01, 2016	Jan. 01, 2015	Dec. 31, 2017	Nov. 30, 2017	Oct. 31, 2017	Sep. 30, 2017	Aug. 31, 2017	Jul. 31, 2017	Jun. 30, 2017	May 31, 2017	Apr. 30, 2017	Mar. 31, 2017	Feb. 28, 2017	Jan. 31, 2017	Dec. 31, 2016	Nov. 30, 2016	Oct. 31, 2016	Sep. 30, 2016	Aug. 31, 2016	Jul. 31, 2016	Jun. 30, 2016	May 31, 2016	Apr. 30, 2016	Mar. 31, 2016	Feb. 29, 2016	Jan. 31, 2016	Dec. 31, 2015	Nov. 30, 2015	Oct. 31, 2015	Sep. 30, 2015	Aug. 31, 2015	Jul. 31, 2015	Jun. 30, 2015	May 31, 2015	Apr. 30, 2015	Mar. 31, 2015	Feb. 28, 2015	Jan. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity [Abstract]
Total Number of Shares Purchased	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	118,746	199,391	211,040	129,849	0	0	160,000	200,000	203,820	100,000	0	0	0	0	1,322,846
Average Price Paid per Share (in dollars per share)	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 22.39	$ 22.11	$ 23.19	$ 23.15	$ 0.00	$ 0.00	$ 24.93	$ 25.59	$ 30.84	$ 31.69	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 25.34
Total Number of Shares Purchased as Part of Publicly Announced Plans or Programs	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	118,746	199,391	211,040	129,849	0	0	160,000	200,000	203,820	100,000	0	0	0	0	1,322,846
Maximum Number of Shares that May Yet Be Purchased Under the Plans or Programs	500,996,000	164,562,000	155,695	780,725,000	780,725,000	780,725,000	779,930,000	779,930,000	779,930,000	779,133,000	757,398,000	745,782,000	744,718,000	744,718,000	744,718,000	500,996,000	500,996,000	500,996,000	500,687,000	500,687,000	500,687,000	495,378,000	481,497,000	481,497,000	480,645,000	480,645,000	480,645,000	164,562	164,562	164,562	164,093	164,093	164,093	164,093	147,289	147,289	213,523	263,523	263,523	780,725,000	500,996,000	164,562
Maximum Number (or Approximate Dollar Value) of Shares that May Yet Be Purchased Under the Plans or Programs	$ 148,008	$ 148,008	$ 15,027,043	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 148,008	$ 2,806,575	$ 7,214,395	$ 12,107,835	$ 15,114,029	$ 15,114,029	$ 15,114,029	$ 4,102,131	$ 9,220,841	$ 13,442,543	$ 15,027,043	$ 15,027,043	$ 148,008	$ 148,008	$ 148,008