Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income	$ 53,620	$ 53,137	$ 42,682	$ 44,090	$ 34,802	$ 21,482	$ 36,624	$ 37,333	$ 193,529	$ 130,241	$ 89,388
Basic weighted average shares (in shares)	195,302,613	196,121,691	196,994,210	196,621,906	196,516,632	196,445,684	196,270,119	196,217,311	196,256,128	196,363,084	195,933,800
Dilutive effect of stock options and RSUs (in shares)									2,662,289	2,985,662	2,113,653
Diluted weighted average shares (in shares)	197,889,189	198,659,459	199,618,809	199,524,913	199,446,875	199,452,308	198,441,315	198,160,465	198,918,417	199,348,746	198,047,453
Basic net income per share (in dollars per share)	$ 0.27	$ 0.27	$ 0.22	$ 0.22	$ 0.18	$ 0.11	$ 0.19	$ 0.19	$ 0.99	$ 0.66	$ 0.46
Diluted net income per share (in dollars per share)	$ 0.27	$ 0.27	$ 0.21	$ 0.22	$ 0.17	$ 0.11	$ 0.18	$ 0.19	$ 0.97	$ 0.65	$ 0.45
Anti-dilutive shares excluded from diluted earnings per share computation (in shares)									512,684	275,194	49,795