Fair Value of Assets and Liabilities - Debt Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Senior Unsecured Notes, due 2022 at 5.00%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	5.00%	5.00%
Senior Unsecured Notes, due 2023 at 4.50%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	4.50%
Senior Unsecured Notes, due 2024 at 4.65%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	4.65%
Senior Unsecured Notes, due 2024 at 4.35%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	4.35%
Senior Unsecured Notes, due 2025 at 4.50%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	4.50%
Senior Unsecured Notes, due 2025 at 7.50%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	7.50%
Senior Unsecured Notes, due 2026 at 5.25%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	5.25%
Senior Unsecured Notes, due 2026 at 4.75%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	4.75%
Senior Unsecured Notes, due 2027 at 4.95%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	4.95%
Senior Unsecured Notes, due 2027 at 5.50%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	5.50%
Senior Unsecured Notes, due 2028 at 3.95%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	3.95%
Senior Unsecured Notes, due 2029 at 4.95%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	4.95%
Senior Unsecured Notes, due 2030 at 4.375%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	4.375%
Carrying Value
Fair Value of Assets and Liabilities
Total financial liabilities	$ 6,139,787	$ 6,130,166
Carrying Value | Senior Unsecured Notes, due 2022 at 5.00%
Fair Value of Assets and Liabilities
Total financial liabilities	498,941	498,032
Carrying Value | Senior Unsecured Notes, due 2023 at 4.50%
Fair Value of Assets and Liabilities
Total financial liabilities	499,720	499,596
Carrying Value | Senior Unsecured Notes, due 2024 at 4.65%
Fair Value of Assets and Liabilities
Total financial liabilities	349,004	348,700
Carrying Value | Senior Unsecured Notes, due 2024 at 4.35%
Fair Value of Assets and Liabilities
Total financial liabilities	820,649	819,546
Carrying Value | Senior Unsecured Notes, due 2025 at 4.50%
Fair Value of Assets and Liabilities
Total financial liabilities	347,634	347,118
Carrying Value | Senior Unsecured Notes, due 2025 at 7.50%
Fair Value of Assets and Liabilities
Total financial liabilities	790,757	789,006
Carrying Value | Senior Unsecured Notes, due 2026 at 5.25%
Fair Value of Assets and Liabilities
Total financial liabilities	345,059	344,212
Carrying Value | Senior Unsecured Notes, due 2026 at 4.75%
Fair Value of Assets and Liabilities
Total financial liabilities	446,973	446,515
Carrying Value | Senior Unsecured Notes, due 2027 at 4.95%
Fair Value of Assets and Liabilities
Total financial liabilities	395,971	395,405
Carrying Value | Senior Unsecured Notes, due 2027 at 5.50%
Fair Value of Assets and Liabilities
Total financial liabilities	443,109	442,370
Carrying Value | Senior Unsecured Notes, due 2028 at 3.95%
Fair Value of Assets and Liabilities
Total financial liabilities	392,770	391,908
Carrying Value | Senior Unsecured Notes, due 2029 at 4.95%
Fair Value of Assets and Liabilities
Total financial liabilities	418,697	418,102
Carrying Value | Senior Unsecured Notes, due 2030 at 4.375%
Fair Value of Assets and Liabilities
Total financial liabilities	390,503	389,656
Fair Value
Fair Value of Assets and Liabilities
Total financial liabilities	6,324,424	6,361,902
Fair Value | Senior Unsecured Notes, due 2022 at 5.00%
Fair Value of Assets and Liabilities
Total financial liabilities	504,458	510,285
Fair Value | Senior Unsecured Notes, due 2023 at 4.50%
Fair Value of Assets and Liabilities
Total financial liabilities	511,435	505,280
Fair Value | Senior Unsecured Notes, due 2024 at 4.65%
Fair Value of Assets and Liabilities
Total financial liabilities	355,541	347,893
Fair Value | Senior Unsecured Notes, due 2024 at 4.35%
Fair Value of Assets and Liabilities
Total financial liabilities	840,362	819,328
Fair Value | Senior Unsecured Notes, due 2025 at 4.50%
Fair Value of Assets and Liabilities
Total financial liabilities	350,656	346,462
Fair Value | Senior Unsecured Notes, due 2025 at 7.50%
Fair Value of Assets and Liabilities
Total financial liabilities	900,748	926,404
Fair Value | Senior Unsecured Notes, due 2026 at 5.25%
Fair Value of Assets and Liabilities
Total financial liabilities	353,668	354,996
Fair Value | Senior Unsecured Notes, due 2026 at 4.75%
Fair Value of Assets and Liabilities
Total financial liabilities	449,460	448,506
Fair Value | Senior Unsecured Notes, due 2027 at 4.95%
Fair Value of Assets and Liabilities
Total financial liabilities	399,028	404,328
Fair Value | Senior Unsecured Notes, due 2027 at 5.50%
Fair Value of Assets and Liabilities
Total financial liabilities	479,815	491,918
Fair Value | Senior Unsecured Notes, due 2028 at 3.95%
Fair Value of Assets and Liabilities
Total financial liabilities	379,540	388,146
Fair Value | Senior Unsecured Notes, due 2029 at 4.95%
Fair Value of Assets and Liabilities
Total financial liabilities	417,163	430,064
Fair Value | Senior Unsecured Notes, due 2030 at 4.375%
Fair Value of Assets and Liabilities
Total financial liabilities	$ 382,550	$ 388,292